C1 Bài 2: Phương trình bậc nhất hai ẩn và hệ hai phương trình bậc nhất hai ẩn

<p><span style="font-size: medium;"> <span face=""Open Sans", Arial, sans-serif" style="box-sizing: border-box; color: green; font-weight: 640; text-align: justify;">Khởi động trang 10 Toán 9 Tập 1: </span><span face=""Open Sans", Arial, sans-serif" style="text-align: justify;">Bài toán cổ:</span></span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: center;"><em style="box-sizing: border-box;"><span style="font-size: medium;">Một đàn em nhỏ đứng bên sông</span></em></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: center;"><em style="box-sizing: border-box;"><span style="font-size: medium;">To nhỏ bàn nhau chuyện chia hồng</span></em></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: center;"><em style="box-sizing: border-box;"><span style="font-size: medium;">Mỗi người năm trái thừa năm trái</span></em></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: center;"><em style="box-sizing: border-box;"><span style="font-size: medium;">Mỗi người sáu trái một người không</span></em></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: center;"><em style="box-sizing: border-box;"><span style="font-size: medium;">Hỡi người bạn trẻ đang dừng bước</span></em></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: center;"><em style="box-sizing: border-box;"><span style="font-size: medium;">Có mấy em thơ, mấy trái hồng?</span></em></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Làm thế nào để tính được số em nhỏ (em thơ) và số trái hồng?</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;"><img alt="Khởi động trang 10 Toán 9 Tập 1 Chân trời sáng tạo | Giải Toán 9" src="https://vietjack.com/toan-9-ct/images/khoi-dong-trang-10-toan-9-tap-1.PNG" style="border: 0px; box-sizing: border-box; display: inline; margin-left: auto; margin-right: auto; max-width: 100%; padding-bottom: 4px; vertical-align: middle;" /></span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; color: green; font-size: medium; font-weight: 640;">Lời giải:</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Gọi x là số em nhỏ, y là số quả hồng (x, y ∈ ℕ*).</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">– Câu “Mỗi người năm trái thừa năm trái” nên ta có 5x = y – 5.          (1)</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">– Câu “Mỗi người sáu trái một người không” nên ta có 6(x – 1) = y.    (2)</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Để tính được số em nhỏ (em thơ) và số trái hồng thì ta tìm giá trị x, y thỏa mãn phương trình (1) và phương trình (2).</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box;"><span style="background-color: white; box-sizing: border-box; color: #990000; font-size: large; font-weight: 640;">1. Phương trình bậc nhất hai ẩn</span></span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Thực hành 1 trang 12 Toán 9 Tập 1: </span>Xác định các hệ số a, b, c của mỗi phương trình bậc nhất hai ẩn sau:</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">a) x + 5y = –4;</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">b) <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mn>3</mn></msqrt><mi>x</mi><mo>+</mo><mi>y</mi><mo>=</mo><mn>0</mn></math>" id="MathJax-Element-1-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-2" style="box-sizing: content-box; display: inline-block;"><span class="mjx-msqrt" id="MJXc-Node-3" style="box-sizing: content-box; display: inline-block;"><span class="mjx-box" style="box-sizing: content-box; display: inline-block; padding-top: 0.045em;"><span class="mjx-surd" style="box-sizing: content-box; display: inline-block; vertical-align: top;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.507em; white-space: pre;">√</span></span><span class="mjx-box" style="border-top: 1.6px solid; box-sizing: content-box; display: inline-block; padding-top: 0.119em;"><span class="mjx-mrow" id="MJXc-Node-4" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-5" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span></span></span></span><span class="mjx-mi" id="MJXc-Node-6" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-7" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mi MJXc-space2" id="MJXc-Node-8" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-9" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-10" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mn>3</mn></msqrt><mi>�</mi><mo>+</mo><mi>�</mi><mo>=</mo><mn>0</mn></math></span></span>;</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">c) <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mi>x</mi><mo>&#x2212;</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>y</mi><mo>=</mo><mn>6</mn></math>" id="MathJax-Element-2-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-11" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-12" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-13" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-14" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-15" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac MJXc-space2" id="MJXc-Node-16" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box; display: block; position: absolute; text-align: center; top: -1.297em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-17" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-18" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box; display: inline-block; height: 1.32em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-19" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-20" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-21" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">6</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mi>�</mi><mo>−</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>�</mi><mo>=</mo><mn>6</mn></math></span></span>;</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">d) 2x + 0y = –1,5.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; color: green; font-size: medium; font-weight: 640;">Lời giải:</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">a) x + 5y = –4 là phương trình bậc nhất hai ẩn với a = 1, b = 5, c = –4.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">b) <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mn>3</mn></msqrt><mi>x</mi><mo>+</mo><mi>y</mi><mo>=</mo><mn>0</mn></math>" id="MathJax-Element-3-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-22" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-23" style="box-sizing: content-box; display: inline-block;"><span class="mjx-msqrt" id="MJXc-Node-24" style="box-sizing: content-box; display: inline-block;"><span class="mjx-box" style="box-sizing: content-box; display: inline-block; padding-top: 0.045em;"><span class="mjx-surd" style="box-sizing: content-box; display: inline-block; vertical-align: top;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.507em; white-space: pre;">√</span></span><span class="mjx-box" style="border-top: 1.6px solid; box-sizing: content-box; display: inline-block; padding-top: 0.119em;"><span class="mjx-mrow" id="MJXc-Node-25" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-26" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span></span></span></span><span class="mjx-mi" id="MJXc-Node-27" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-28" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mi MJXc-space2" id="MJXc-Node-29" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-30" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-31" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mn>3</mn></msqrt><mi>�</mi><mo>+</mo><mi>�</mi><mo>=</mo><mn>0</mn></math></span></span> là phương trình bậc nhất hai ẩn với <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>=</mo><msqrt><mn>3</mn></msqrt><mo>,</mo><mtext>&#xA0;</mtext><mi>b</mi><mo>=</mo><mn>1,</mn><mtext>&#xA0;</mtext><mi>c</mi><mo>=</mo><mn>0</mn></math>" id="MathJax-Element-4-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-32" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-33" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-34" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">a</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-35" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-msqrt MJXc-space3" id="MJXc-Node-36" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-box" style="box-sizing: content-box; display: inline-block; padding-top: 0.045em;"><span class="mjx-surd" style="box-sizing: content-box; display: inline-block; vertical-align: top;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.507em; white-space: pre;">√</span></span><span class="mjx-box" style="border-top: 1.6px solid; box-sizing: content-box; display: inline-block; padding-top: 0.119em;"><span class="mjx-mrow" id="MJXc-Node-37" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-38" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span></span></span></span><span class="mjx-mo" id="MJXc-Node-39" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; margin-top: -0.181em; padding-bottom: 0.553em; white-space: pre;">,</span></span><span class="mjx-mtext MJXc-space1" id="MJXc-Node-40" style="box-sizing: content-box; display: inline-block; margin-left: 0.167em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; margin-top: -0.273em; padding-bottom: 0.324em; white-space: pre;"> </span></span><span class="mjx-mi" id="MJXc-Node-41" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.461em; white-space: pre;">b</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-42" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-43" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.37em; white-space: pre;">1,</span></span><span class="mjx-mtext" id="MJXc-Node-44" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; margin-top: -0.273em; padding-bottom: 0.324em; white-space: pre;"> </span></span><span class="mjx-mi" id="MJXc-Node-45" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">c</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-46" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-47" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><msqrt><mn>3</mn></msqrt><mo>,</mo><mtext> </mtext><mi>�</mi><mo>=</mo><mn>1,</mn><mtext> </mtext><mi>�</mi><mo>=</mo><mn>0</mn></math></span></span>.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">c) <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mi>x</mi><mo>&#x2212;</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>y</mi><mo>=</mo><mn>6</mn></math>" id="MathJax-Element-5-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-48" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-49" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-50" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-51" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-52" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac MJXc-space2" id="MJXc-Node-53" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box; display: block; position: absolute; text-align: center; top: -1.297em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-54" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-55" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box; display: inline-block; height: 1.32em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-56" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-57" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-58" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">6</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mi>�</mi><mo>−</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>�</mi><mo>=</mo><mn>6</mn></math></span></span> là phương trình bậc nhất hai ẩn với <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>=</mo><mn>0,</mn><mtext>&#xA0;</mtext><mi>b</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mo>,</mo><mtext>&#xA0;</mtext><mi>c</mi><mo>=</mo><mn>6</mn></math>" id="MathJax-Element-6-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-59" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-60" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-61" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">a</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-62" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-63" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.37em; white-space: pre;">0,</span></span><span class="mjx-mtext" id="MJXc-Node-64" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; margin-top: -0.273em; padding-bottom: 0.324em; white-space: pre;"> </span></span><span class="mjx-mi" id="MJXc-Node-65" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.461em; white-space: pre;">b</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-66" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-67" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-68" style="box-sizing: content-box; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box; display: block; position: absolute; text-align: center; top: -1.297em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-69" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-70" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box; display: inline-block; height: 1.32em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mo" id="MJXc-Node-71" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; margin-top: -0.181em; padding-bottom: 0.553em; white-space: pre;">,</span></span><span class="mjx-mtext MJXc-space1" id="MJXc-Node-72" style="box-sizing: content-box; display: inline-block; margin-left: 0.167em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; margin-top: -0.273em; padding-bottom: 0.324em; white-space: pre;"> </span></span><span class="mjx-mi" id="MJXc-Node-73" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">c</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-74" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-75" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">6</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mn>0,</mn><mtext> </mtext><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mo>,</mo><mtext> </mtext><mi>�</mi><mo>=</mo><mn>6</mn></math></span></span>.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box;"><span style="background-color: white; box-sizing: border-box; font-size: medium; font-weight: 640;"></span></span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">d) 2x + 0y = –1,5 là phương trình bậc nhất hai ẩn với a = 2, b = 0, c = –1,5.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Thực hành 2 trang 12 Toán 9 Tập 1: </span>Cho phương trình 3x + 2y = 4. (1)</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">a) Trong hai cặp số (1; 2) và (2; –1), cặp số nào là nghiệm của phương trình (1)?</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">b) Tìm y<span style="bottom: -0.25em; box-sizing: border-box; line-height: 0; position: relative; vertical-align: baseline;">0</span> để cặp số (4; y<span style="bottom: -0.25em; box-sizing: border-box; line-height: 0; position: relative; vertical-align: baseline;">0</span>) là nghiệm của phương trình (1).</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">c) Tìm thêm hai nghiệm của phương trình (1).</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">d) Hãy biểu diễn tất cả các nghiệm của phương trình (1) trên mặt phẳng tọa độ Oxy.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; color: green; font-size: medium; font-weight: 640;">Lời giải:</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">a) Cặp số (1; 2) không phải là nghiệm của phương trình (1) vì 3 . 1 + 2 . 2 = 3 + 4 = 7 ≠ 4.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">Cặp số (2; –1) là nghiệm của phương trình (1) vì 3 . 2 + 2 . (–1) = 6 – 2 = 4.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">Vậy trong hai cặp số đã cho, cặp số (2; –1) là nghiệm của phương trình (1).</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">b) Để cặp số (4; y<span style="bottom: -0.25em; box-sizing: border-box; line-height: 0; position: relative; vertical-align: baseline;">0</span>) là nghiệm của phương trình (1) thì</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">3 . 4 + 2y<span style="bottom: -0.25em; box-sizing: border-box; line-height: 0; position: relative; vertical-align: baseline;">0</span> = 4 hay 12 + 2y<span style="bottom: -0.25em; box-sizing: border-box; line-height: 0; position: relative; vertical-align: baseline;">0</span> = 4 suy ra y<span style="bottom: -0.25em; box-sizing: border-box; line-height: 0; position: relative; vertical-align: baseline;">0</span> = –4.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">c) Tìm thêm hai nghiệm của phương trình (1).</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">• Thay x = 0 vào phương trình (1), ta có:</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">3 . 0 + 2y = 4 hay 2y = 4 suy ra y = 2.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">• Thay x = –2 vào phương trình (1), ta có:</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">3 . (–2) + 2y = 4 hay –6 + 2y = 4 suy ra y = 5.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">Vậy hai nghiệm của phương trình (1) khác với các nghiệm trên là (0; 2) và (–2; 5).</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">d) Viết phương trình 3x + 2y = 4 thành <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>x</mi><mo>+</mo><mn>2</mn></math>" id="MathJax-Element-1-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-2" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-3" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-4" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-5" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-6" style="box-sizing: content-box; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box; display: block; position: absolute; text-align: center; top: -1.297em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-7" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-8" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box; display: inline-block; height: 1.32em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-9" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-10" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-11" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>�</mi><mo>+</mo><mn>2</mn></math></span></span>.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">Khi đó, tất cả các nghiệm của phương trình đã cho được biểu diễn bởi đường thẳng d: <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>x</mi><mo>+</mo><mn>2</mn></math>" id="MathJax-Element-2-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-12" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-13" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-14" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-15" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-16" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-17" style="box-sizing: content-box; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box; display: block; position: absolute; text-align: center; top: -1.297em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-18" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-19" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box; display: inline-block; height: 1.32em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-20" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-21" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-22" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>�</mi><mo>+</mo><mn>2</mn></math></span></span>.</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">Phương trình (1) có nghiệm là (0; 2) và (2; –1) nên đường thẳng d: <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>x</mi><mo>+</mo><mn>2</mn></math>" id="MathJax-Element-3-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-23" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-24" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-25" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-26" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-27" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-28" style="box-sizing: content-box; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box; display: block; position: absolute; text-align: center; top: -1.297em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-29" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-30" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box; display: inline-block; height: 1.32em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-31" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-32" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-33" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>�</mi><mo>+</mo><mn>2</mn></math></span></span> đi qua hai điểm A(0; 2) và B(2; –1).</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">Vậy ta có biểu diễn tất cả các nghiệm của phương trình (1) trên mặt phẳng tọa độ Oxy như sau:</span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;"></span></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><img alt="Thực hành 2 trang 12 Toán 9 Tập 1 Chân trời sáng tạo | Giải Toán 9" height="212" src="https://vietjack.com/toan-9-ct/images/a-sua-thuc-hanh-2-trang-12-toan-9-tap-1-1.PNG" style="border: 0px; box-sizing: border-box; display: block; margin-left: auto; margin-right: auto; max-width: 100%; padding-bottom: 4px; vertical-align: middle;" width="188" /></p><p style="box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; color: #990000; font-size: large; font-weight: 640;">2. Hệ hai phương trình bậc nhất hai ẩn</span></p><ul class="list" style="box-sizing: border-box; color: #313131; font-family: "Open Sans", Arial, sans-serif; margin: 15px 0px; overflow: hidden; padding: 0px;"><li style="background-attachment: initial; background-clip: initial; background-image: initial; background-origin: initial; background-position: 0px 0px; background-repeat: initial; background-size: initial; box-sizing: border-box; color: black; line-height: 24px; list-style: none; margin-bottom: 7px; padding: 0px; text-align: left;"></li></ul><ul class="list" style="box-sizing: border-box; color: #313131; font-family: "Open Sans", Arial, sans-serif; margin: 15px 0px; overflow: hidden; padding: 0px;"><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Khám phá 2 trang 12 Toán 9 Tập 1: </span>Một ô tô từ A đến B, cùng lúc đó một xe máy đi từ B về A. Gọi x (km/h) là tốc độ của ô tô, y (km/h) là tốc độ của xe máy (x > 0, y > 0). Biết rằng:</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">(1) Tốc độ của ô tô hơn tốc độ xe máy 15 km/h;</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">(2) Quãng đường AB dài 210 km và hai xe gặp nhau sau 2 giờ.</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">a) Từ dữ kiện (1), hãy lập một phương trình hai ẩn x, y?</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">b) Từ dữ kiện (2), hãy lập thêm một phương trình hai ẩn x, y?</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">c) Bạn An khẳng định rằng tốc độ của ô tô và xe máy lần lượt là 60 km/h và 45 km/h. Có thể dùng hai phương trình lập được để kiểm tra khẳng định của bạn An là đúng hay sai không?</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; color: green; font-size: medium; font-weight: 640;">Lời giải:</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">a) Từ dữ kiện (1), ta lập được phương trình là: x – y = 15.          (3)</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">b) Quãng đường đi được của ô tô sau 2 giờ là: 2x (km)</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Quãng đường đi được của xe máy sau 2 giờ là: 2y (km)</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Một ô tô từ A đến B, cùng lúc đó một xe máy đi từ B về A nghĩa là ô tô và xe máy chuyển động ngược chiều nên 2x + 2y = 210 (km).</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Vậy từ dữ kiện (2), ta lập được phương trình là: 2x + 2y = 210 hay x + y = 105.      (4)</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">c) Khi tốc độ của ô tô và xe máy lần lượt là 60 km/h và 45 km/h thì x = 60 km/h và y = 45 km/h.</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">• Thay x = 60, y = 45 vào phương trình (3), ta có:</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">x – y = 60 – 45 = 15.</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">• Thay x = 60, y = 45 vào phương trình (4), ta có:</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">x + y = 60 + 45 = 105.</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Vậy ta có thể dùng hai phương trình lập được để kiểm tra khẳng định của bạn An và ta thấy khẳng định của bạn An là đúng.</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Thực hành 3 trang 14 Toán 9 Tập 1: </span>Trong các hệ phương trình sau, hệ phương trình nào là hệ hai phương trình bậc nhất hai ẩn?</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">a) <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mi>x</mi><mo>+</mo><mn>3</mn><mi>y</mi><mo>=</mo><mn>0</mn></mtd></mtr><mtr><mtd><mn>4</mn><mi>x</mi><mo>&#x2212;</mo><mn>3</mn><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>4</mn><mo>;</mo></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-1-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-2" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-3" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-5" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" face="MJXc-TeX-size3-R, MJXc-TeX-size3-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-6" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.001em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 134.625px;"><span class="mjx-mtr" id="MJXc-Node-7" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-8" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 6.18em;"><span class="mjx-mrow" id="MJXc-Node-9" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mi" id="MJXc-Node-10" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-11" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-12" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mi" id="MJXc-Node-13" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-14" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-15" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-16" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-17" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-18" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-19" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-mi" id="MJXc-Node-20" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-21" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-22" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mi" id="MJXc-Node-23" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-24" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-25" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-26" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-mo" id="MJXc-Node-27" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.14em; white-space: pre;">;</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mi>�</mi><mo>+</mo><mn>3</mn><mi>�</mi><mo>=</mo><mn>0</mn></mtd></mtr><mtr><mtd><mn>4</mn><mi>�</mi><mo>−</mo><mn>3</mn><mi>�</mi><mo>=</mo><mo>−</mo><mn>4</mn><mo>;</mo></mtd></mtr></mtable></mfenced></math></span></span></span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">b) <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><msqrt><mn>3</mn></msqrt><mi>x</mi><mo>+</mo><mn>0</mn><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>5</mn></mtd></mtr><mtr><mtd><mn>0</mn><mi>x</mi><mo>+</mo><mfrac><mn>4</mn><mn>5</mn></mfrac><mi>y</mi><mo>=</mo><mn>3</mn><mo>;</mo></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-2-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-28" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-29" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-30" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-31" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size4-R" face="MJXc-TeX-size4-R, MJXc-TeX-size4-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.517em; padding-top: 1.517em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-32" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.215em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 146.719px;"><span class="mjx-mtr" id="MJXc-Node-33" style="box-sizing: content-box; display: table-row; height: 1.38em;"><span class="mjx-mtd" id="MJXc-Node-34" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 6.735em;"><span class="mjx-mrow" id="MJXc-Node-35" style="box-sizing: content-box; display: inline-block; margin-top: -0.071em;"><span class="mjx-msqrt" id="MJXc-Node-36" style="box-sizing: content-box; display: inline-block;"><span class="mjx-box" style="box-sizing: content-box; display: inline-block; padding-top: 0.045em;"><span class="mjx-surd" style="box-sizing: content-box; display: inline-block; vertical-align: top;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.507em; white-space: pre;">√</span></span><span class="mjx-box" style="border-top: 1.6px solid; box-sizing: content-box; display: inline-block; padding-top: 0.119em;"><span class="mjx-mrow" id="MJXc-Node-37" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-38" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span></span></span></span><span class="mjx-mi" id="MJXc-Node-39" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-40" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-41" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-42" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-43" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-44" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-45" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-46" style="box-sizing: content-box; display: table-row; height: 1.549em;"><span class="mjx-mtd" id="MJXc-Node-47" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-48" style="box-sizing: content-box; display: inline-block; margin-top: -0.09em;"><span class="mjx-mn" id="MJXc-Node-49" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-50" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-51" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mfrac MJXc-space2" id="MJXc-Node-52" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box; display: block; position: absolute; text-align: center; top: -1.287em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-53" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span></span><span class="mjx-denominator" style="bottom: -0.591em; box-sizing: content-box; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-54" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box; display: inline-block; height: 1.328em; vertical-align: -0.418em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-55" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-56" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-57" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mo" id="MJXc-Node-58" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.14em; white-space: pre;">;</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><msqrt><mn>3</mn></msqrt><mi>�</mi><mo>+</mo><mn>0</mn><mi>�</mi><mo>=</mo><mo>−</mo><mn>5</mn></mtd></mtr><mtr><mtd><mn>0</mn><mi>�</mi><mo>+</mo><mfrac><mn>4</mn><mn>5</mn></mfrac><mi>�</mi><mo>=</mo><mn>3</mn><mo>;</mo></mtd></mtr></mtable></mfenced></math></span></span></span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;">c) <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mn>7</mn><mi>x</mi><mo>+</mo><mn>2</mn><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>5</mn></mtd></mtr><mtr><mtd><mn>0</mn><mi>x</mi><mo>+</mo><mn>0</mn><mi>y</mi><mo>=</mo><mn>9.</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-3-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-59" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-60" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-61" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-62" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" face="MJXc-TeX-size3-R, MJXc-TeX-size3-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-63" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.001em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 128.563px;"><span class="mjx-mtr" id="MJXc-Node-64" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-65" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 5.902em;"><span class="mjx-mrow" id="MJXc-Node-66" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-67" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">7</span></span><span class="mjx-mi" id="MJXc-Node-68" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-69" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-70" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mi" id="MJXc-Node-71" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-72" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-73" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-74" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-75" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-76" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-77" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-78" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-79" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-80" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-81" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-82" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-83" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-84" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">9.</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mn>7</mn><mi>�</mi><mo>+</mo><mn>2</mn><mi>�</mi><mo>=</mo><mo>−</mo><mn>5</mn></mtd></mtr><mtr><mtd><mn>0</mn><mi>�</mi><mo>+</mo><mn>0</mn><mi>�</mi><mo>=</mo><mn>9.</mn></mtd></mtr></mtable></mfenced></math></span></span></span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; color: green; font-size: medium; font-weight: 640;">Lời giải:</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">a) Hệ phương trình <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mi>x</mi><mo>+</mo><mn>3</mn><mi>y</mi><mo>=</mo><mn>0</mn></mtd></mtr><mtr><mtd><mn>4</mn><mi>x</mi><mo>&#x2212;</mo><mn>3</mn><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>4</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-4-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-85" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-86" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-87" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-88" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" face="MJXc-TeX-size3-R, MJXc-TeX-size3-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-89" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.001em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 128.563px;"><span class="mjx-mtr" id="MJXc-Node-90" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-91" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 5.902em;"><span class="mjx-mrow" id="MJXc-Node-92" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mi" id="MJXc-Node-93" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-94" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-95" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mi" id="MJXc-Node-96" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-97" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-98" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-99" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-100" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-101" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-102" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-mi" id="MJXc-Node-103" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-104" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-105" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mi" id="MJXc-Node-106" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-107" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-108" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-109" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mi>�</mi><mo>+</mo><mn>3</mn><mi>�</mi><mo>=</mo><mn>0</mn></mtd></mtr><mtr><mtd><mn>4</mn><mi>�</mi><mo>−</mo><mn>3</mn><mi>�</mi><mo>=</mo><mo>−</mo><mn>4</mn></mtd></mtr></mtable></mfenced></math></span></span> là hệ phương trình bậc nhất hai ẩn với a = 1, b = 3, c = 0, a<em style="box-sizing: border-box;">'</em> = 4, b<em style="box-sizing: border-box;">'</em> = –3, c<em style="box-sizing: border-box;">'</em> = –4.</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">b) Hệ phương trình <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><msqrt><mn>3</mn></msqrt><mi>x</mi><mo>+</mo><mn>0</mn><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>5</mn></mtd></mtr><mtr><mtd><mn>0</mn><mi>x</mi><mo>+</mo><mfrac><mn>4</mn><mn>5</mn></mfrac><mi>y</mi><mo>=</mo><mn>3</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-5-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-110" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-111" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-112" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-113" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size4-R" face="MJXc-TeX-size4-R, MJXc-TeX-size4-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.517em; padding-top: 1.517em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-114" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.215em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 146.719px;"><span class="mjx-mtr" id="MJXc-Node-115" style="box-sizing: content-box; display: table-row; height: 1.38em;"><span class="mjx-mtd" id="MJXc-Node-116" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 6.735em;"><span class="mjx-mrow" id="MJXc-Node-117" style="box-sizing: content-box; display: inline-block; margin-top: -0.071em;"><span class="mjx-msqrt" id="MJXc-Node-118" style="box-sizing: content-box; display: inline-block;"><span class="mjx-box" style="box-sizing: content-box; display: inline-block; padding-top: 0.045em;"><span class="mjx-surd" style="box-sizing: content-box; display: inline-block; vertical-align: top;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.507em; white-space: pre;">√</span></span><span class="mjx-box" style="border-top: 1.6px solid; box-sizing: content-box; display: inline-block; padding-top: 0.119em;"><span class="mjx-mrow" id="MJXc-Node-119" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-120" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span></span></span></span><span class="mjx-mi" id="MJXc-Node-121" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-122" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-123" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-124" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-125" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-126" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-127" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-128" style="box-sizing: content-box; display: table-row; height: 1.549em;"><span class="mjx-mtd" id="MJXc-Node-129" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-130" style="box-sizing: content-box; display: inline-block; margin-top: -0.09em;"><span class="mjx-mn" id="MJXc-Node-131" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-132" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-133" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mfrac MJXc-space2" id="MJXc-Node-134" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box; display: block; position: absolute; text-align: center; top: -1.287em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-135" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span></span><span class="mjx-denominator" style="bottom: -0.591em; box-sizing: content-box; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-136" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box; display: inline-block; height: 1.328em; vertical-align: -0.418em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-137" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-138" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-139" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><msqrt><mn>3</mn></msqrt><mi>�</mi><mo>+</mo><mn>0</mn><mi>�</mi><mo>=</mo><mo>−</mo><mn>5</mn></mtd></mtr><mtr><mtd><mn>0</mn><mi>�</mi><mo>+</mo><mfrac><mn>4</mn><mn>5</mn></mfrac><mi>�</mi><mo>=</mo><mn>3</mn></mtd></mtr></mtable></mfenced></math></span></span> là hệ phương trình bậc nhất hai ẩn với <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>=</mo><msqrt><mn>3</mn></msqrt><mo>,</mo></math>" id="MathJax-Element-6-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-140" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-141" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-142" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">a</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-143" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-msqrt MJXc-space3" id="MJXc-Node-144" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-box" style="box-sizing: content-box; display: inline-block; padding-top: 0.045em;"><span class="mjx-surd" style="box-sizing: content-box; display: inline-block; vertical-align: top;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.553em; padding-top: 0.507em; white-space: pre;">√</span></span><span class="mjx-box" style="border-top: 1.6px solid; box-sizing: content-box; display: inline-block; padding-top: 0.119em;"><span class="mjx-mrow" id="MJXc-Node-145" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-146" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span></span></span></span><span class="mjx-mo" id="MJXc-Node-147" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; margin-top: -0.181em; padding-bottom: 0.553em; white-space: pre;">,</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><msqrt><mn>3</mn></msqrt><mo>,</mo></math></span></span> b = 0, c = –5, a<em style="box-sizing: border-box;">'</em> = 0, <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>'</mo><mo>=</mo><mfrac><mn>4</mn><mn>5</mn></mfrac><mo>,</mo></math>" id="MathJax-Element-7-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-148" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-149" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-150" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.461em; white-space: pre;">b</span></span><span class="mjx-mo" id="MJXc-Node-151" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.416em; white-space: pre;">'</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-152" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mfrac MJXc-space3" id="MJXc-Node-153" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box; display: block; position: absolute; text-align: center; top: -1.287em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-154" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span></span><span class="mjx-denominator" style="bottom: -0.591em; box-sizing: content-box; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-155" style="box-sizing: content-box; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box; display: inline-block; height: 1.328em; vertical-align: -0.418em; width: 0px;"></span></span><span class="mjx-mo" id="MJXc-Node-156" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; margin-top: -0.181em; padding-bottom: 0.553em; white-space: pre;">,</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>'</mo><mo>=</mo><mfrac><mn>4</mn><mn>5</mn></mfrac><mo>,</mo></math></span></span> c<em style="box-sizing: border-box;">'</em> = 3.</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;"></span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">c) Hệ phương trình <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mn>7</mn><mi>x</mi><mo>+</mo><mn>2</mn><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>5</mn></mtd></mtr><mtr><mtd><mn>0</mn><mi>x</mi><mo>+</mo><mn>0</mn><mi>y</mi><mo>=</mo><mn>9</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-8-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-157" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-158" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-159" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-160" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" face="MJXc-TeX-size3-R, MJXc-TeX-size3-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-161" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.001em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 128.563px;"><span class="mjx-mtr" id="MJXc-Node-162" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-163" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 5.902em;"><span class="mjx-mrow" id="MJXc-Node-164" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-165" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">7</span></span><span class="mjx-mi" id="MJXc-Node-166" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-167" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-168" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mi" id="MJXc-Node-169" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-170" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-171" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-172" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-173" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-174" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-175" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-176" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-177" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-178" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-179" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-180" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-181" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-182" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">9</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mn>7</mn><mi>�</mi><mo>+</mo><mn>2</mn><mi>�</mi><mo>=</mo><mo>−</mo><mn>5</mn></mtd></mtr><mtr><mtd><mn>0</mn><mi>�</mi><mo>+</mo><mn>0</mn><mi>�</mi><mo>=</mo><mn>9</mn></mtd></mtr></mtable></mfenced></math></span></span> không phải là hệ phương trình bậc nhất hai ẩn vì a<em style="box-sizing: border-box;">'</em> = b<em style="box-sizing: border-box;">'</em> = 0.</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Thực hành 4 trang 14 Toán 9 Tập 1: </span>Cho hệ phương trình <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mi>x</mi><mo>+</mo><mn>5</mn><mi>y</mi><mo>=</mo><mn>10</mn></mtd></mtr><mtr><mtd><mn>2</mn><mi>x</mi><mo>&#x2212;</mo><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>13.</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-1-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-2" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-3" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-5" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" face="MJXc-TeX-size3-R, MJXc-TeX-size3-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-6" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.001em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 134.625px;"><span class="mjx-mtr" id="MJXc-Node-7" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-8" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 6.18em;"><span class="mjx-mrow" id="MJXc-Node-9" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mi" id="MJXc-Node-10" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-11" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-12" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-mi" id="MJXc-Node-13" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-14" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-15" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">10</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-16" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-17" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-18" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-19" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mi" id="MJXc-Node-20" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-21" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mi MJXc-space2" id="MJXc-Node-22" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-23" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-24" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-25" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">13.</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mi>�</mi><mo>+</mo><mn>5</mn><mi>�</mi><mo>=</mo><mn>10</mn></mtd></mtr><mtr><mtd><mn>2</mn><mi>�</mi><mo>−</mo><mi>�</mi><mo>=</mo><mo>−</mo><mn>13.</mn></mtd></mtr></mtable></mfenced></math></span></span>. Trong hai cặp số (0; 2) và (–5; 3), cặp số nào là nghiệm của hệ phương trình đã cho?</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; color: green; font-size: medium; font-weight: 640;">Lời giải:</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Cặp số (0; 2) không phải là nghiệm của hệ phương trình đã cho vì <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mfenced><mrow><mo>&#x2212;</mo><mn>5</mn></mrow></mfenced><mo>+</mo><mn>5</mn><mo>&#x22C5;</mo><mn>3</mn><mo>=</mo><mn>10</mn></mtd></mtr><mtr><mtd><mn>2</mn><mo>&#x22C5;</mo><mfenced><mrow><mo>&#x2212;</mo><mn>5</mn></mrow></mfenced><mo>&#x2212;</mo><mn>3</mn><mo>=</mo><mo>&#x2212;</mo><mn>13.</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-2-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-26" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-27" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-28" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-29" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" face="MJXc-TeX-size3-R, MJXc-TeX-size3-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-30" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.046em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 182.766px;"><span class="mjx-mtr" id="MJXc-Node-31" style="box-sizing: content-box; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-32" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 8.39em;"><span class="mjx-mrow" id="MJXc-Node-33" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mfenced" id="MJXc-Node-34" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-35" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-36" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-37" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-38" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-mo" id="MJXc-Node-39" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-40" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-41" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-42" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-43" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-44" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-45" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">10</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-46" style="box-sizing: content-box; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-47" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-48" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-49" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-50" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mfenced MJXc-space2" id="MJXc-Node-51" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-mo" id="MJXc-Node-52" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-53" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-54" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-55" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-mo" id="MJXc-Node-56" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-57" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-58" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-59" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-60" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-61" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">13.</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mfenced><mrow><mo>−</mo><mn>5</mn></mrow></mfenced><mo>+</mo><mn>5</mn><mo>⋅</mo><mn>3</mn><mo>=</mo><mn>10</mn></mtd></mtr><mtr><mtd><mn>2</mn><mo>⋅</mo><mfenced><mrow><mo>−</mo><mn>5</mn></mrow></mfenced><mo>−</mo><mn>3</mn><mo>=</mo><mo>−</mo><mn>13.</mn></mtd></mtr></mtable></mfenced></math></span></span></span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Cặp số (–5; 3) là nghiệm của hệ phương trình đã cho vì <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mfenced><mrow><mo>&#x2212;</mo><mn>5</mn></mrow></mfenced><mo>+</mo><mn>5</mn><mo>&#x22C5;</mo><mn>5</mn><mo>=</mo><mn>10</mn></mtd></mtr><mtr><mtd><mn>2</mn><mo>&#x22C5;</mo><mfenced><mrow><mo>&#x2212;</mo><mn>5</mn></mrow></mfenced><mo>&#x2212;</mo><mn>3</mn><mo>=</mo><mo>&#x2212;</mo><mn>13.</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-3-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-62" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-63" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-64" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-65" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" face="MJXc-TeX-size3-R, MJXc-TeX-size3-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-66" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.046em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 182.766px;"><span class="mjx-mtr" id="MJXc-Node-67" style="box-sizing: content-box; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-68" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 8.39em;"><span class="mjx-mrow" id="MJXc-Node-69" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mfenced" id="MJXc-Node-70" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-71" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-72" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-73" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-74" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-mo" id="MJXc-Node-75" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-76" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-77" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-78" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-79" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-80" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-81" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">10</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-82" style="box-sizing: content-box; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-83" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-84" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-85" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-86" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mfenced MJXc-space2" id="MJXc-Node-87" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-mo" id="MJXc-Node-88" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-89" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-90" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-91" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-mo" id="MJXc-Node-92" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-93" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-94" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-95" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-96" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-97" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">13.</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block; height: 1px; left: 0px; overflow: hidden; padding: 1px 0px 0px; position: absolute; top: 0px; user-select: none; width: 1px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mfenced><mrow><mo>−</mo><mn>5</mn></mrow></mfenced><mo>+</mo><mn>5</mn><mo>⋅</mo><mn>5</mn><mo>=</mo><mn>10</mn></mtd></mtr><mtr><mtd><mn>2</mn><mo>⋅</mo><mfenced><mrow><mo>−</mo><mn>5</mn></mrow></mfenced><mo>−</mo><mn>3</mn><mo>=</mo><mo>−</mo><mn>13.</mn></mtd></mtr></mtable></mfenced></math></span></span></span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;"></span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Vậy trong hai cặp số (0; 2) và (–5; 3), cặp số (–5; 3) là nghiệm của hệ phương trình đã cho.</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Vận dụng trang 14 Toán 9 Tập 1: </span>Đối với bài toán trong <span style="box-sizing: border-box; font-weight: 700;">Hoạt động khởi động (trang 10)</span>, nếu gọi x là số em nhỏ, y là số quả hồng thì ta nhận được hệ hai phương trình bậc nhất hai ẩn nào?</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; color: green; font-size: medium; font-weight: 640;">Lời giải:</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Gọi x là số em nhỏ, y là số quả hồng (x, y ∈ ℕ*).</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Câu “Mỗi người năm trái thừa năm trái” nên ta có 5x = y – 5 hay 5x – y = –5.          (1)</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Câu “Mỗi người sáu trái một người không” nên ta có 6(x – 1) = y hay 6x – y = 6.    (2)</span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;"></span></p><p style="box-sizing: border-box; color: black; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px; text-align: justify;"><span style="box-sizing: border-box; font-size: medium;">Từ (1) và (2) ta có hệ hai phương trình bậc nhất hai ẩn <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mn>5</mn><mi>x</mi><mo>&#x2212;</mo><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>5</mn></mtd></mtr><mtr><mtd><mn>6</mn><mi>x</mi><mo>&#x2212;</mo><mi>y</mi><mo>=</mo><mn>6.</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-1-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-2" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-3" style="box-sizing: content-box; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-5" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" face="MJXc-TeX-size3-R, MJXc-TeX-size3-Rw" style="box-sizing: content-box; display: block; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-6" style="box-sizing: content-box; display: inline-block; padding: 0px 0.167em; vertical-align: -1.001em;"><span class="mjx-table" style="box-sizing: content-box; display: table; width: 117.672px;"><span class="mjx-mtr" id="MJXc-Node-7" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-8" style="box-sizing: content-box; display: table-cell; padding: 0px; width: 5.402em;"><span class="mjx-mrow" id="MJXc-Node-9" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-10" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-mi" id="MJXc-Node-11" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-12" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mi MJXc-space2" id="MJXc-Node-13" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-14" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-15" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-16" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-17" style="box-sizing: content-box; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-18" style="box-sizing: content-box; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-19" style="box-sizing: content-box; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-20" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">6</span></span><span class="mjx-mi" id="MJXc-Node-21" style="box-sizing: content-box; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-22" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mi MJXc-space2" id="MJXc-Node-23" style="box-sizing: content-box; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-math-I" face="MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw" style="box-sizing: content-box; display: block; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-24" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-25" style="box-sizing: content-box; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" face="MJXc-TeX-main-R, MJXc-TeX-main-Rw" style="box-sizing: content-box; display: block; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">6.</span></span><span class="mjx-strut" style="box-sizing: content-box; display: inline-block; padding-top: 1em; width: 0px;"><br /><br /><br /><br /></span></span></span></span></span></span></span></span></span></span></span></p></ul><span style="background-color: white; box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; font-weight: 640; text-align: justify;"><span style="font-size: medium;">Bài tập</span></span><div><span style="background-color: white; box-sizing: border-box; font-family: "Open Sans", Arial, sans-serif; font-weight: 640; text-align: justify;"><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Bài 1 trang 14 Toán 9 Tập 1: </span>Trong các phương trình sau, phương trình nào là phương trình bậc nhất hai ẩn? Xác định các hệ số a, b, c của mỗi phương trình bậc nhất hai ẩn đó.</span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) 2x + 5y = –7;</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">b) 0x – 0y = 5;</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">c) <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mi>x</mi><mo>&#x2212;</mo><mfrac><mn>5</mn><mn>4</mn></mfrac><mi>y</mi><mo>=</mo><mn>3</mn></math>" id="MathJax-Element-1-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-2" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-3" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-4" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-5" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac MJXc-space2" id="MJXc-Node-6" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box !important; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box !important; display: block; position: absolute; text-align: center; top: -1.298em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-7" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-denominator" style="bottom: -0.58em; box-sizing: content-box !important; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-8" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box !important; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box !important; display: inline-block; height: 1.328em; vertical-align: -0.41em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-9" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-10" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-11" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mi>�</mi><mo>−</mo><mfrac><mn>5</mn><mn>4</mn></mfrac><mi>�</mi><mo>=</mo><mn>3</mn></math></span></span>;</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">d) 0,2x + 0y = –1,5.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box; color: green; font-weight: 640;"><span style="font-size: medium;">Lời giải:</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) 2x + 5y = –7 là phương trình bậc nhất hai ẩn với a = 2, b = 5, c = –7.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">b) 0x – 0y = 5 không phải là phương trình bậc nhất hai ẩn vì a = 0 và b = 0.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">c) <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mi>x</mi><mo>&#x2212;</mo><mfrac><mn>5</mn><mn>4</mn></mfrac><mi>y</mi><mo>=</mo><mn>3</mn></math>" id="MathJax-Element-2-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-12" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-13" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mn" id="MJXc-Node-14" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span><span class="mjx-mi" id="MJXc-Node-15" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-16" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac MJXc-space2" id="MJXc-Node-17" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box !important; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box !important; display: block; position: absolute; text-align: center; top: -1.298em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-18" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-denominator" style="bottom: -0.58em; box-sizing: content-box !important; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-19" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box !important; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box !important; display: inline-block; height: 1.328em; vertical-align: -0.41em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-20" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-21" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-22" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mi>�</mi><mo>−</mo><mfrac><mn>5</mn><mn>4</mn></mfrac><mi>�</mi><mo>=</mo><mn>3</mn></math></span></span> là phương trình bậc nhất hai ẩn với <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>=</mo><mn>0,</mn><mtext>&#xA0;</mtext><mi>b</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>5</mn><mn>4</mn></mfrac><mo>,</mo><mtext>&#xA0;</mtext><mi>c</mi><mo>=</mo><mn>3</mn></math>" id="MathJax-Element-3-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-23" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-24" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-25" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">a</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-26" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-27" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.553em; padding-top: 0.37em; white-space: pre;">0,</span></span><span class="mjx-mtext" id="MJXc-Node-28" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-top: -0.273em; padding-bottom: 0.324em; white-space: pre;"> </span></span><span class="mjx-mi" id="MJXc-Node-29" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.461em; white-space: pre;">b</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-30" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-31" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-32" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box !important; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box !important; display: block; position: absolute; text-align: center; top: -1.298em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-33" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">5</span></span></span><span class="mjx-denominator" style="bottom: -0.58em; box-sizing: content-box !important; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-34" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box !important; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box !important; display: inline-block; height: 1.328em; vertical-align: -0.41em; width: 0px;"></span></span><span class="mjx-mo" id="MJXc-Node-35" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-top: -0.181em; padding-bottom: 0.553em; white-space: pre;">,</span></span><span class="mjx-mtext MJXc-space1" id="MJXc-Node-36" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.167em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-top: -0.273em; padding-bottom: 0.324em; white-space: pre;"> </span></span><span class="mjx-mi" id="MJXc-Node-37" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">c</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-38" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-39" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mn>0,</mn><mtext> </mtext><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>5</mn><mn>4</mn></mfrac><mo>,</mo><mtext> </mtext><mi>�</mi><mo>=</mo><mn>3</mn></math></span></span>.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">d) 0,2x + 0y = –1,5 là phương trình bậc nhất hai ẩn với a = 0,2; b = 0; c = –1,5.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Bài 2 trang 14 Toán 9 Tập 1: </span>Trong các cặp số (1; 1), (–2; 5), (0; 2), cặp số nào là nghiệm của mỗi phương trình sau?</span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) 4x + 3y = 7;</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">b) 3x – 4y = –1.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box; color: green; font-weight: 640;"><span style="font-size: medium;">Lời giải:</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) Cặp số (1; 1) là nghiệm của phương trình 4x + 3y = 7 vì 4 . 1 + 3 . 1 = 4 + 3 = 7.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Cặp số (–2; 5) là nghiệm của phương trình 4x + 3y = 7 vì 4 . (–2) + 3 . 5 = –8 + 15 = 7.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Cặp số (0; 2) không phải là nghiệm của phương trình 4x + 3y = 7 vì 4 . 0 + 3 . 2 = 6 ≠ 7.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Vậy trong các cặp số đã cho thì có hai cặp số (1; 1) và (–2; 5) là nghiệm của phương trình 4x + 3y = 7.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) Cặp số (1; 1) là nghiệm của phương trình 3x – 4y = –1 vì 3 . 1 – 4 . 1 = 3 – 4 = –1.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Cặp số (–2; 5) không phải là nghiệm của phương trình 3x – 4y = –1 vì 3 . (–2) – 4 . 5 = -6 – 20 = –26 ≠ –1.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Cặp số (0; 2) không phải là nghiệm của phương trình 3x – 4y = –1 vì 3 . 0 – 4 . 2 = 0 – 8 = –8 ≠ –1.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><span style="box-sizing: border-box;"></span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Vậy trong các cặp số đã cho thì có cặp số (1; 1) là nghiệm của phương trình 3x – 4y = –1.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Bài 3 trang 14 Toán 9 Tập 1: </span>Hãy biểu diễn tất cả các nghiệm của mỗi phương trình sau trên mặt phẳng tọa độ Oxy.</span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) 2x + y = 3;</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">b) 0x – y = 3;</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">c) –3x + 0y = 2;</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">d) –2x + y = 0.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box; color: green; font-weight: 640;"><span style="font-size: medium;">Lời giải:</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) Viết lại phương trình thành y = –2x + 3.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Từ đó, tất cả các nghiệm của phương trình đã cho được biểu diễn bởi đường thẳng d: y = –2x + 3 (như hình vẽ).</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><img alt="Bài 3 trang 14 Toán 9 Tập 1 Chân trời sáng tạo | Giải Toán 9" src="https://vietjack.com/toan-9-ct/images/bai-3-trang-14-toan-lop-9-tap-1.PNG" style="border: 0px; box-sizing: border-box; display: inline; margin-left: auto; margin-right: auto; max-width: 100%; padding-bottom: 4px; vertical-align: middle;" /></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">b) Viết lại phương trình thành y = –3.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Từ đó, tất cả các nghiệm của phương trình đã cho được biểu diễn bởi đường thẳng d vuông góc với Oy tại điểm M(0; –3).</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><img alt="Bài 3 trang 14 Toán 9 Tập 1 Chân trời sáng tạo | Giải Toán 9" src="https://vietjack.com/toan-9-ct/images/bai-3-trang-14-toan-lop-9-tap-1a.PNG" style="border: 0px; box-sizing: border-box; display: inline; margin-left: auto; margin-right: auto; max-width: 100%; padding-bottom: 4px; vertical-align: middle;" /></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">c) Viết lại phương trình thành <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>x</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>2</mn><mn>3</mn></mfrac></math>" id="MathJax-Element-1-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-2" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-3" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-4" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-5" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-6" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box !important; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box !important; display: block; position: absolute; text-align: center; top: -1.276em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-7" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-denominator" style="bottom: -0.59em; box-sizing: content-box !important; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-8" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box !important; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box !important; display: inline-block; height: 1.32em; vertical-align: -0.417em; width: 0px;"></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>2</mn><mn>3</mn></mfrac></math></span></span>.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Từ đó, tất cả các nghiệm của phương trình đã cho được biểu diễn bởi đường thẳng d vuông góc với Ox tại điểm <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>N</mi><mfenced><mrow><mo>&#x2212;</mo><mfrac><mn>2</mn><mn>3</mn></mfrac><mo>;</mo><mtext>&#x2009;&#x2009;</mtext><mn>0</mn></mrow></mfenced></math>" id="MathJax-Element-2-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-9" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-10" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-11" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-right: 0.085em; padding-top: 0.461em; white-space: pre;">N</span></span><span class="mjx-mfenced MJXc-space1" id="MJXc-Node-12" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.167em;"><span class="mjx-mo" id="MJXc-Node-13" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-size1-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-size1-R, MJXc-TeX-size1-Rw; padding-bottom: 0.645em; padding-top: 0.645em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-14" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-15" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-16" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box !important; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box !important; display: block; position: absolute; text-align: center; top: -1.276em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-17" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-denominator" style="bottom: -0.59em; box-sizing: content-box !important; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-18" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box !important; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box !important; display: inline-block; height: 1.32em; vertical-align: -0.417em; width: 0px;"></span></span><span class="mjx-mo" id="MJXc-Node-19" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.553em; padding-top: 0.14em; white-space: pre;">;</span></span><span class="mjx-mtext MJXc-space1" id="MJXc-Node-20" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.167em;"><span class="mjx-char" style="box-sizing: content-box !important; display: block; white-space: pre;"><span class="mjx-charbox MJXc-TeX-main-R" style="box-sizing: content-box !important; display: inline-block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-right: 0.167em;"></span><span class="mjx-charbox MJXc-TeX-main-R" style="box-sizing: content-box !important; display: inline-block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-right: 0.167em;"></span></span></span><span class="mjx-mn" id="MJXc-Node-21" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">0</span></span></span><span class="mjx-mo" id="MJXc-Node-22" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-size1-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-size1-R, MJXc-TeX-size1-Rw; padding-bottom: 0.645em; padding-top: 0.645em; white-space: pre;">)</span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mfenced><mrow><mo>−</mo><mfrac><mn>2</mn><mn>3</mn></mfrac><mo>;</mo><mtext>  </mtext><mn>0</mn></mrow></mfenced></math></span></span>.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><img alt="Bài 3 trang 14 Toán 9 Tập 1 Chân trời sáng tạo | Giải Toán 9" src="https://vietjack.com/toan-9-ct/images/bai-3-trang-14-toan-lop-9-tap-1b.PNG" style="border: 0px; box-sizing: border-box; display: inline; margin-left: auto; margin-right: auto; max-width: 100%; padding-bottom: 4px; vertical-align: middle;" /></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">d) Viết lại phương trình thành y = 2x.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Từ đó, tất cả các nghiệm của phương trình đã cho được biểu diễn bởi đường thẳng d: y = 2x</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Đường thẳng d đi qua gốc tọa độ O và điểm A(1; 2) (như hình vẽ).</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><span style="box-sizing: border-box;"></span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><img alt="Bài 3 trang 14 Toán 9 Tập 1 Chân trời sáng tạo | Giải Toán 9" src="https://vietjack.com/toan-9-ct/images/bai-3-trang-14-toan-lop-9-tap-1c.PNG" style="border: 0px; box-sizing: border-box; display: inline; margin-left: auto; margin-right: auto; max-width: 100%; padding-bottom: 4px; vertical-align: middle;" /></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Bài 4 trang 14 Toán 9 Tập 1: </span>Cho hệ phương trình <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mn>4</mn><mi>x</mi><mo>&#x2212;</mo><mi>y</mi><mo>=</mo><mn>2</mn></mtd></mtr><mtr><mtd><mi>x</mi><mo>+</mo><mn>3</mn><mi>y</mi><mo>=</mo><mn>7.</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-1-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-2" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-3" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-5" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-size3-R, MJXc-TeX-size3-Rw; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-6" style="box-sizing: content-box !important; display: inline-block; padding: 0px 0.167em; vertical-align: -1.001em;"><span class="mjx-table" style="box-sizing: content-box !important; display: table; width: 106.781px;"><span class="mjx-mtr" id="MJXc-Node-7" style="box-sizing: content-box !important; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-8" style="box-sizing: content-box !important; display: table-cell; padding: 0px; width: 4.902em;"><span class="mjx-mrow" id="MJXc-Node-9" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-10" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-mi" id="MJXc-Node-11" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-12" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mi MJXc-space2" id="MJXc-Node-13" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-14" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-15" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-16" style="box-sizing: content-box !important; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-17" style="box-sizing: content-box !important; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-18" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mi" id="MJXc-Node-19" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-20" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-21" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mi" id="MJXc-Node-22" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-23" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-24" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">7.</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mn>4</mn><mi>�</mi><mo>−</mo><mi>�</mi><mo>=</mo><mn>2</mn></mtd></mtr><mtr><mtd><mi>�</mi><mo>+</mo><mn>3</mn><mi>�</mi><mo>=</mo><mn>7.</mn></mtd></mtr></mtable></mfenced></math></span></span>. Cặp số nào dưới đây là nghiệm của hệ phương trình đã cho?</span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) (2; 2);</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">b) (1; 2);</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">c) (–1; –2).</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box; color: green; font-weight: 640;"><span style="font-size: medium;">Lời giải:</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) Cặp số (2; 2) không phải là nghiệm của hệ phương trình đã cho vì <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mn>4</mn><mo>&#x22C5;</mo><mn>2</mn><mo>&#x2212;</mo><mn>2</mn><mo>=</mo><mn>6</mn><mtext>&#x2009;&#x2009;</mtext><mfenced><mrow><mo>&#x2260;</mo><mn>2</mn></mrow></mfenced></mtd></mtr><mtr><mtd><mn>2</mn><mo>+</mo><mn>3</mn><mo>&#x22C5;</mo><mn>2</mn><mo>=</mo><mn>8</mn><mtext>&#x2009;&#x2009;</mtext><mfenced><mrow><mo>&#x2260;</mo><mn>7</mn></mrow></mfenced><mo>.</mo></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-2-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-25" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-26" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-27" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-28" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-size3-R, MJXc-TeX-size3-Rw; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-29" style="box-sizing: content-box !important; display: inline-block; padding: 0px 0.167em; vertical-align: -1.046em;"><span class="mjx-table" style="box-sizing: content-box !important; display: table; width: 182.75px;"><span class="mjx-mtr" id="MJXc-Node-30" style="box-sizing: content-box !important; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-31" style="box-sizing: content-box !important; display: table-cell; padding: 0px; width: 8.391em;"><span class="mjx-mrow" id="MJXc-Node-32" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-33" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-34" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-35" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-36" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-37" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-38" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-39" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">6</span></span><span class="mjx-mtext" id="MJXc-Node-40" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char" style="box-sizing: content-box !important; display: block; white-space: pre;"><span class="mjx-charbox MJXc-TeX-main-R" style="box-sizing: content-box !important; display: inline-block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-right: 0.167em;"></span><span class="mjx-charbox MJXc-TeX-main-R" style="box-sizing: content-box !important; display: inline-block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-right: 0.167em;"></span></span></span><span class="mjx-mfenced MJXc-space1" id="MJXc-Node-41" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.167em;"><span class="mjx-mo" id="MJXc-Node-42" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-43" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-44" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.553em; padding-top: 0.416em; white-space: pre;">≠</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-45" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-mo" id="MJXc-Node-46" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-47" style="box-sizing: content-box !important; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-48" style="box-sizing: content-box !important; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-49" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-50" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-51" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-52" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-53" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-54" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-55" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-56" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">8</span></span><span class="mjx-mtext" id="MJXc-Node-57" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char" style="box-sizing: content-box !important; display: block; white-space: pre;"><span class="mjx-charbox MJXc-TeX-main-R" style="box-sizing: content-box !important; display: inline-block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-right: 0.167em;"></span><span class="mjx-charbox MJXc-TeX-main-R" style="box-sizing: content-box !important; display: inline-block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-right: 0.167em;"></span></span></span><span class="mjx-mfenced MJXc-space1" id="MJXc-Node-58" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.167em;"><span class="mjx-mo" id="MJXc-Node-59" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-60" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-61" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.553em; padding-top: 0.416em; white-space: pre;">≠</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-62" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">7</span></span></span><span class="mjx-mo" id="MJXc-Node-63" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo" id="MJXc-Node-64" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-top: -0.181em; padding-bottom: 0.324em; white-space: pre;">.</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mn>4</mn><mo>⋅</mo><mn>2</mn><mo>−</mo><mn>2</mn><mo>=</mo><mn>6</mn><mtext>  </mtext><mfenced><mrow><mo>≠</mo><mn>2</mn></mrow></mfenced></mtd></mtr><mtr><mtd><mn>2</mn><mo>+</mo><mn>3</mn><mo>⋅</mo><mn>2</mn><mo>=</mo><mn>8</mn><mtext>  </mtext><mfenced><mrow><mo>≠</mo><mn>7</mn></mrow></mfenced><mo>.</mo></mtd></mtr></mtable></mfenced></math></span></span></span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">b) Cặp số (1; 2) là nghiệm của hệ phương trình đã cho vì <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mn>4</mn><mo>&#x22C5;</mo><mn>1</mn><mo>&#x2212;</mo><mn>2</mn><mo>=</mo><mn>2</mn></mtd></mtr><mtr><mtd><mn>1</mn><mo>+</mo><mn>3</mn><mo>&#x22C5;</mo><mn>2</mn><mo>=</mo><mn>7.</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-3-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-65" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-66" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-67" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-68" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-size3-R, MJXc-TeX-size3-Rw; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-69" style="box-sizing: content-box !important; display: inline-block; padding: 0px 0.167em; vertical-align: -0.971em;"><span class="mjx-table" style="box-sizing: content-box !important; display: table; width: 121px;"><span class="mjx-mtr" id="MJXc-Node-70" style="box-sizing: content-box !important; display: table-row; height: 1.221em;"><span class="mjx-mtd" id="MJXc-Node-71" style="box-sizing: content-box !important; display: table-cell; padding: 0px; width: 5.556em;"><span class="mjx-mrow" id="MJXc-Node-72" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-73" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-74" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-75" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-76" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-77" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-78" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-79" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-80" style="box-sizing: content-box !important; display: table-row; height: 1.221em;"><span class="mjx-mtd" id="MJXc-Node-81" style="box-sizing: content-box !important; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-82" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-83" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-84" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-85" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-86" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-87" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-88" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-89" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">7.</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mn>4</mn><mo>⋅</mo><mn>1</mn><mo>−</mo><mn>2</mn><mo>=</mo><mn>2</mn></mtd></mtr><mtr><mtd><mn>1</mn><mo>+</mo><mn>3</mn><mo>⋅</mo><mn>2</mn><mo>=</mo><mn>7.</mn></mtd></mtr></mtable></mfenced></math></span></span></span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">c) Cặp số (–1; –2) không phải là nghiệm của hệ phương trình đã cho vì <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mn>4</mn><mo>&#x22C5;</mo><mfenced><mrow><mo>&#x2212;</mo><mn>1</mn></mrow></mfenced><mo>&#x2212;</mo><mfenced><mrow><mo>&#x2212;</mo><mn>2</mn></mrow></mfenced><mo>=</mo><mo>&#x2212;</mo><mn>2</mn><mtext>&#x2009;</mtext><mfenced><mrow><mo>&#x2260;</mo><mn>2</mn></mrow></mfenced></mtd></mtr><mtr><mtd><mfenced><mrow><mo>&#x2212;</mo><mn>1</mn></mrow></mfenced><mo>+</mo><mn>3</mn><mo>&#x22C5;</mo><mfenced><mrow><mo>&#x2212;</mo><mn>2</mn></mrow></mfenced><mo>=</mo><mo>&#x2212;</mo><mn>7</mn><mtext>&#x2009;&#x2009;</mtext><mfenced><mrow><mo>&#x2260;</mo><mn>7</mn></mrow></mfenced><mo>.</mo></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-4-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-90" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-91" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-92" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-93" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-size3-R, MJXc-TeX-size3-Rw; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-94" style="box-sizing: content-box !important; display: inline-block; padding: 0px 0.167em; vertical-align: -1.046em;"><span class="mjx-table" style="box-sizing: content-box !important; display: table; width: 267.531px;"><span class="mjx-mtr" id="MJXc-Node-95" style="box-sizing: content-box !important; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-96" style="box-sizing: content-box !important; display: table-cell; padding: 0px; width: 12.281em;"><span class="mjx-mrow" id="MJXc-Node-97" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-98" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-99" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mfenced MJXc-space2" id="MJXc-Node-100" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-mo" id="MJXc-Node-101" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-102" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-103" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-104" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span></span><span class="mjx-mo" id="MJXc-Node-105" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-106" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfenced MJXc-space2" id="MJXc-Node-107" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-mo" id="MJXc-Node-108" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-109" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-110" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-111" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-mo" id="MJXc-Node-112" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-113" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-114" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-115" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mtext" id="MJXc-Node-116" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char" style="box-sizing: content-box !important; display: block; white-space: pre;"><span class="mjx-charbox MJXc-TeX-main-R" style="box-sizing: content-box !important; display: inline-block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-right: 0.167em;"></span></span></span><span class="mjx-mfenced MJXc-space1" id="MJXc-Node-117" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.167em;"><span class="mjx-mo" id="MJXc-Node-118" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-119" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-120" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.553em; padding-top: 0.416em; white-space: pre;">≠</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-121" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-mo" id="MJXc-Node-122" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-123" style="box-sizing: content-box !important; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-124" style="box-sizing: content-box !important; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-125" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mfenced" id="MJXc-Node-126" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-127" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-128" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-129" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-130" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span></span><span class="mjx-mo" id="MJXc-Node-131" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-132" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-133" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-134" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mfenced MJXc-space2" id="MJXc-Node-135" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-mo" id="MJXc-Node-136" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-137" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-138" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-139" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-mo" id="MJXc-Node-140" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-141" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-142" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-143" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">7</span></span><span class="mjx-mtext" id="MJXc-Node-144" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char" style="box-sizing: content-box !important; display: block; white-space: pre;"><span class="mjx-charbox MJXc-TeX-main-R" style="box-sizing: content-box !important; display: inline-block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-right: 0.167em;"></span><span class="mjx-charbox MJXc-TeX-main-R" style="box-sizing: content-box !important; display: inline-block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-right: 0.167em;"></span></span></span><span class="mjx-mfenced MJXc-space1" id="MJXc-Node-145" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.167em;"><span class="mjx-mo" id="MJXc-Node-146" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-147" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-148" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.553em; padding-top: 0.416em; white-space: pre;">≠</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-149" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">7</span></span></span><span class="mjx-mo" id="MJXc-Node-150" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo" id="MJXc-Node-151" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; margin-top: -0.181em; padding-bottom: 0.324em; white-space: pre;">.</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"><br /><br /></span></span></span></span></span></span></span></span></span></span></span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><span style="box-sizing: border-box; color: green; font-weight: 640;">Bài 5 trang 14 Toán 9 Tập 1: </span>Cho hai đường thẳng <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>x</mi><mo>+</mo><mn>2</mn></math>" id="MathJax-Element-1-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-1" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-2" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-3" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-4" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-5" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-6" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box !important; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box !important; display: block; position: absolute; text-align: center; top: -1.276em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-7" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box !important; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-8" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box !important; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box !important; display: inline-block; height: 1.305em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-9" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-10" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-11" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>�</mi><mo>+</mo><mn>2</mn></math></span></span> và y = –2x – 1.</span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) Vẽ hai đường thẳng đó trên cùng mặt phẳng tọa độ Oxy.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">b) Xác định tọa độ giao điểm A của hai đường thẳng trên.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">c) Tọa độ của điểm A có là nghiệm của hệ phương trình <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mi>x</mi><mo>+</mo><mn>2</mn><mi>y</mi><mo>=</mo><mn>4</mn></mtd></mtr><mtr><mtd><mn>2</mn><mi>x</mi><mo>+</mo><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>1</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-2-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-12" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-13" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-14" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-16" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-size3-R, MJXc-TeX-size3-Rw; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-17" style="box-sizing: content-box !important; display: inline-block; padding: 0px 0.167em; vertical-align: -1.001em;"><span class="mjx-table" style="box-sizing: content-box !important; display: table; width: 117.672px;"><span class="mjx-mtr" id="MJXc-Node-18" style="box-sizing: content-box !important; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-19" style="box-sizing: content-box !important; display: table-cell; padding: 0px; width: 5.402em;"><span class="mjx-mrow" id="MJXc-Node-20" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mi" id="MJXc-Node-21" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-22" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-23" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mi" id="MJXc-Node-24" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-25" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-26" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-27" style="box-sizing: content-box !important; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-28" style="box-sizing: content-box !important; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-29" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-30" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mi" id="MJXc-Node-31" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-32" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mi MJXc-space2" id="MJXc-Node-33" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-34" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-35" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-36" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mi>�</mi><mo>+</mo><mn>2</mn><mi>�</mi><mo>=</mo><mn>4</mn></mtd></mtr><mtr><mtd><mn>2</mn><mi>�</mi><mo>+</mo><mi>�</mi><mo>=</mo><mo>−</mo><mn>1</mn></mtd></mtr></mtable></mfenced></math></span></span> không? Tại sao?</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box; color: green; font-weight: 640;"><span style="font-size: medium;">Lời giải:</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">a) Đường thẳng <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>x</mi><mo>+</mo><mn>2</mn></math>" id="MathJax-Element-3-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-37" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-38" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-39" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-40" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-41" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-42" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box !important; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box !important; display: block; position: absolute; text-align: center; top: -1.276em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-43" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box !important; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-44" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box !important; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box !important; display: inline-block; height: 1.305em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-45" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-46" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-47" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>�</mi><mo>+</mo><mn>2</mn></math></span></span> đi qua điểm M(0; 2) và điểm N(2; 1).</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Đường thẳng y = –2x – 1 đi qua điểm P(0; –1) và điểm Q(–1; 1).</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Ta vẽ hai đường thẳng đó trên cùng mặt phẳng tọa độ Oxy như sau:</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><img alt="Bài 5 trang 14 Toán 9 Tập 1 Chân trời sáng tạo | Giải Toán 9" src="https://vietjack.com/toan-9-ct/images/bai-5-trang-14-toan-lop-9-tap-1.PNG" style="border: 0px; box-sizing: border-box; display: inline; margin-left: auto; margin-right: auto; max-width: 100%; padding-bottom: 4px; vertical-align: middle;" /></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">b) Giao điểm A của hai đường thẳng <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>x</mi><mo>+</mo><mn>2</mn></math>" id="MathJax-Element-4-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-48" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-49" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-50" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-51" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-52" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-53" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box !important; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box !important; display: block; position: absolute; text-align: center; top: -1.276em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-54" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box !important; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-55" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box !important; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box !important; display: inline-block; height: 1.305em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-56" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-57" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-58" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>�</mi><mo>+</mo><mn>2</mn></math></span></span> và y = –2x – 1 được biểu diễn như sau:</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><img alt="Bài 5 trang 14 Toán 9 Tập 1 Chân trời sáng tạo | Giải Toán 9" src="https://vietjack.com/toan-9-ct/images/bai-5-trang-14-toan-lop-9-tap-1a.PNG" style="border: 0px; box-sizing: border-box; display: inline; margin-left: auto; margin-right: auto; max-width: 100%; padding-bottom: 4px; vertical-align: middle;" /></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Dóng điểm A lên hai trục Ox và Oy, ta có A(–2; 3).</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Vậy tọa độ giao điểm A của hai đường thẳng <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>x</mi><mo>+</mo><mn>2</mn></math>" id="MathJax-Element-5-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-59" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-60" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mi" id="MJXc-Node-61" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-62" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-63" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mfrac" id="MJXc-Node-64" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-box MJXc-stacked" style="box-sizing: content-box !important; display: inline-block; height: 0px; padding: 0px 0.12em; position: relative; width: 0.495em;"><span class="mjx-numerator" style="box-sizing: content-box !important; display: block; position: absolute; text-align: center; top: -1.276em; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-65" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span></span><span class="mjx-denominator" style="bottom: -0.569em; box-sizing: content-box !important; display: block; position: absolute; text-align: center; width: 0.7em;"><span class="mjx-mn" id="MJXc-Node-66" style="box-sizing: content-box !important; display: inline-block; text-align: left;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-line" style="border-bottom: 1.3px solid; box-sizing: content-box !important; display: block; height: 0px; position: absolute; top: -0.28em; width: 0.495em;"></span></span><span class="mjx-vsize" style="box-sizing: content-box !important; display: inline-block; height: 1.305em; vertical-align: -0.402em; width: 0px;"></span></span><span class="mjx-mi" id="MJXc-Node-67" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-68" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-69" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>�</mi><mo>=</mo><mo>−</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>�</mi><mo>+</mo><mn>2</mn></math></span></span> và y = –2x – 1 là A(–2; 3).</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">c) Cặp số (–2; 3) là nghiệm của hệ phương trình đã cho vì <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mfenced><mrow><mo>&#x2212;</mo><mn>2</mn></mrow></mfenced><mo>+</mo><mn>2</mn><mo>&#x22C5;</mo><mn>3</mn><mo>=</mo><mn>4</mn></mtd></mtr><mtr><mtd><mn>2</mn><mo>&#x22C5;</mo><mfenced><mrow><mo>&#x2212;</mo><mn>2</mn></mrow></mfenced><mo>+</mo><mn>3</mn><mo>=</mo><mo>&#x2212;</mo><mn>1</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-6-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-70" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-71" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-72" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-73" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-size3-R, MJXc-TeX-size3-Rw; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-74" style="box-sizing: content-box !important; display: inline-block; padding: 0px 0.167em; vertical-align: -1.046em;"><span class="mjx-table" style="box-sizing: content-box !important; display: table; width: 165.813px;"><span class="mjx-mtr" id="MJXc-Node-75" style="box-sizing: content-box !important; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-76" style="box-sizing: content-box !important; display: table-cell; padding: 0px; width: 7.612em;"><span class="mjx-mrow" id="MJXc-Node-77" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mfenced" id="MJXc-Node-78" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-79" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-80" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-81" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-82" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-mo" id="MJXc-Node-83" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-84" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-85" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-86" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-87" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-88" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-89" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-90" style="box-sizing: content-box !important; display: table-row; height: 1.296em;"><span class="mjx-mtd" id="MJXc-Node-91" style="box-sizing: content-box !important; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-92" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-93" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-94" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.002em; white-space: pre;">⋅</span></span><span class="mjx-mfenced MJXc-space2" id="MJXc-Node-95" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-mo" id="MJXc-Node-96" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">(</span></span><span class="mjx-mrow" id="MJXc-Node-97" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-98" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-99" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span></span><span class="mjx-mo" id="MJXc-Node-100" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.599em; padding-top: 0.461em; white-space: pre;">)</span></span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-101" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-102" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.37em; padding-top: 0.37em; white-space: pre;">3</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-103" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-104" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-105" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mfenced><mrow><mo>−</mo><mn>2</mn></mrow></mfenced><mo>+</mo><mn>2</mn><mo>⋅</mo><mn>3</mn><mo>=</mo><mn>4</mn></mtd></mtr><mtr><mtd><mn>2</mn><mo>⋅</mo><mfenced><mrow><mo>−</mo><mn>2</mn></mrow></mfenced><mo>+</mo><mn>3</mn><mo>=</mo><mo>−</mo><mn>1</mn></mtd></mtr></mtable></mfenced></math></span></span>.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="box-sizing: border-box;"><span style="font-size: medium;">Do đó, tọa độ của điểm A có là nghiệm của hệ phương trình <span class="mjx-chtml MathJax_CHTML" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mi>x</mi><mo>+</mo><mn>2</mn><mi>y</mi><mo>=</mo><mn>4</mn></mtd></mtr><mtr><mtd><mn>2</mn><mi>x</mi><mo>+</mo><mi>y</mi><mo>=</mo><mo>&#x2212;</mo><mn>1</mn></mtd></mtr></mtable></mfenced></math>" id="MathJax-Element-7-Frame" role="presentation" style="border: 0px; box-sizing: border-box; direction: ltr; display: inline-block; float: none; line-height: 0; margin: 0px; max-height: none; max-width: none; min-height: 0px; min-width: 0px; overflow-wrap: normal; padding: 1px 0px; position: relative; text-align: left; white-space: nowrap; word-spacing: normal;" tabindex="0"><span aria-hidden="true" class="mjx-math" id="MJXc-Node-106" style="border-collapse: separate; border-spacing: 0px; box-sizing: border-box; display: inline-block;"><span class="mjx-mrow" id="MJXc-Node-107" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mfenced" id="MJXc-Node-108" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-mo" id="MJXc-Node-109" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-size3-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-size3-R, MJXc-TeX-size3-Rw; padding-bottom: 1.242em; padding-top: 1.242em; white-space: pre;">{</span></span><span class="mjx-mtable" id="MJXc-Node-110" style="box-sizing: content-box !important; display: inline-block; padding: 0px 0.167em; vertical-align: -1.001em;"><span class="mjx-table" style="box-sizing: content-box !important; display: table; width: 117.672px;"><span class="mjx-mtr" id="MJXc-Node-111" style="box-sizing: content-box !important; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-112" style="box-sizing: content-box !important; display: table-cell; padding: 0px; width: 5.402em;"><span class="mjx-mrow" id="MJXc-Node-113" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mi" id="MJXc-Node-114" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-115" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mn MJXc-space2" id="MJXc-Node-116" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mi" id="MJXc-Node-117" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-118" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mn MJXc-space3" id="MJXc-Node-119" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">4</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span><span class="mjx-mtr" id="MJXc-Node-120" style="box-sizing: content-box !important; display: table-row; height: 1.251em;"><span class="mjx-mtd" id="MJXc-Node-121" style="box-sizing: content-box !important; display: table-cell; padding: 0.221em 0px 0px;"><span class="mjx-mrow" id="MJXc-Node-122" style="box-sizing: content-box !important; display: inline-block; margin-top: -0.2em;"><span class="mjx-mn" id="MJXc-Node-123" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">2</span></span><span class="mjx-mi" id="MJXc-Node-124" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.278em; padding-top: 0.232em; white-space: pre;">x</span></span><span class="mjx-mo MJXc-space2" id="MJXc-Node-125" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">+</span></span><span class="mjx-mi MJXc-space2" id="MJXc-Node-126" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.222em;"><span class="mjx-char MJXc-TeX-math-I" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-math-I, MJXc-TeX-math-Ix, MJXc-TeX-math-Iw; padding-bottom: 0.461em; padding-right: 0.006em; padding-top: 0.232em; white-space: pre;">y</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-127" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.094em; white-space: pre;">=</span></span><span class="mjx-mo MJXc-space3" id="MJXc-Node-128" style="box-sizing: content-box !important; display: inline-block; margin-left: 0.278em;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.416em; padding-top: 0.278em; white-space: pre;">−</span></span><span class="mjx-mn" id="MJXc-Node-129" style="box-sizing: content-box !important; display: inline-block;"><span class="mjx-char MJXc-TeX-main-R" style="box-sizing: content-box !important; display: block; font-family: MJXc-TeX-main-R, MJXc-TeX-main-Rw; padding-bottom: 0.324em; padding-top: 0.37em; white-space: pre;">1</span></span><span class="mjx-strut" style="box-sizing: content-box !important; display: inline-block; padding-top: 1em; width: 0px;"></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation" style="border: 0px !important; box-sizing: border-box; clip: rect(1px, 1px, 1px, 1px); display: block !important; height: 1px !important; left: 0px; overflow: hidden !important; padding: 1px 0px 0px !important; position: absolute !important; top: 0px; user-select: none; width: 1px !important;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced close="" open="{"><mtable columnalign="left"><mtr><mtd><mi>�</mi><mo>+</mo><mn>2</mn><mi>�</mi><mo>=</mo><mn>4</mn></mtd></mtr><mtr><mtd><mn>2</mn><mi>�</mi><mo>+</mo><mi>�</mi><mo>=</mo><mo>−</mo><mn>1</mn></mtd></mtr></mtable></mfenced></math></span></span>.</span></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><br /></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><span style="font-size: medium;"><br /></span></p><p style="box-sizing: border-box; font-weight: 400; line-height: 24px; margin: 0px 0.2em 1em; overflow-wrap: break-word; padding: 0px;"><br /></p></span></div>

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