Ôn tập chương IV
Hướng dẫn giải Bài 58 (Trang 63 SGK Toán Đại số 9, Tập 2)
<p>Giải c&aacute;c phương tr&igrave;nh:</p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo>&#160;</mo><mn>1</mn><mo>,</mo><mn>2</mn><msup><mi>x</mi><mn>3</mn></msup><mo>-</mo><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>0</mn><mo>,</mo><mn>2</mn><mi>x</mi><mo>=</mo><mn>0</mn><mspace linebreak="newline"/><mi>b</mi><mo>)</mo><mo>&#160;</mo><mn>5</mn><msup><mi>x</mi><mn>3</mn></msup><mo>-</mo><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>5</mn><mi>x</mi><mo>+</mo><mn>1</mn><mo>=</mo><mn>0</mn></math></p> <p><strong>Giải:&nbsp;</strong></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo>&#160;</mo><mn>1</mn><mo>,</mo><mn>2</mn><msup><mi>x</mi><mn>3</mn></msup><mo>-</mo><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>0</mn><mo>,</mo><mn>2</mn><mi>x</mi><mo>=</mo><mn>0</mn><mo>&#8660;</mo><mi>x</mi><mfenced><mrow><mn>1</mn><mo>,</mo><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mi>x</mi><mo>-</mo><mn>0</mn><mo>,</mo><mn>2</mn></mrow></mfenced><mo>=</mo><mn>0</mn><mspace linebreak="newline"/><mo>&#8660;</mo><mo>[</mo><mtable><mtr><mtd><mi>x</mi><mo>=</mo><mn>0</mn></mtd></mtr><mtr><mtd><mn>1</mn><mo>,</mo><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mi>x</mi><mo>-</mo><mn>0</mn><mo>,</mo><mn>2</mn><mo>=</mo><mn>0</mn></mtd></mtr></mtable><mtable><mtr><mtd><mfenced><mn>1</mn></mfenced></mtd></mtr><mtr><mtd><mfenced><mn>2</mn></mfenced></mtd></mtr></mtable><mspace linebreak="newline"/><mfenced><mn>1</mn></mfenced><mo>&#8660;</mo><msub><mi>x</mi><mn>1</mn></msub><mo>=</mo><mn>0</mn></math></p> <p>(2) thỏa m&atilde;n điều kiện <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>+</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>-</mo><mn>1</mn><mo>-</mo><mn>0</mn><mo>,</mo><mn>2</mn><mo>=</mo><mn>0</mn></math> n&ecirc;n c&oacute; hai nghiệm <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>x</mi><mn>2</mn></msub><mo>=</mo><mn>1</mn><mo>,</mo><mo>&#160;</mo><msub><mi>x</mi><mn>3</mn></msub><mo>=</mo><mo>-</mo><mfrac><mrow><mn>0</mn><mo>,</mo><mn>2</mn></mrow><mrow><mn>1</mn><mo>,</mo><mn>2</mn></mrow></mfrac><mo>=</mo><mo>-</mo><mfrac><mn>1</mn><mn>6</mn></mfrac></math></p> <p>Phương tr&igrave;nh c&oacute; ba nghiệm: <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>x</mi><mn>1</mn></msub><mo>=</mo><mn>0</mn><mo>,</mo><mo>&#160;</mo><msub><mi>x</mi><mn>2</mn></msub><mo>=</mo><mn>1</mn><mo>,</mo><mo>&#160;</mo><msub><mi>x</mi><mn>3</mn></msub><mo>=</mo><mo>-</mo><mfrac><mn>1</mn><mn>6</mn></mfrac></math></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo>&#160;</mo><mn>5</mn><msup><mi>x</mi><mn>3</mn></msup><mo>-</mo><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>5</mn><mi>x</mi><mo>+</mo><mn>1</mn><mo>=</mo><mn>0</mn><mo>&#8660;</mo><msup><mi>x</mi><mn>2</mn></msup><mfenced><mrow><mn>5</mn><mi>x</mi><mo>-</mo><mn>1</mn></mrow></mfenced><mo>-</mo><mfenced><mrow><mn>5</mn><mi>x</mi><mo>-</mo><mn>1</mn></mrow></mfenced><mo>=</mo><mn>0</mn><mo>&#8660;</mo><mfenced><mrow><mn>5</mn><mi>x</mi><mo>-</mo><mn>1</mn></mrow></mfenced><mfenced><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>1</mn></mrow></mfenced><mo>=</mo><mn>0</mn><mspace linebreak="newline"/><mo>&#8660;</mo><mo>[</mo><mtable><mtr><mtd><mn>5</mn><mi>x</mi><mo>-</mo><mn>1</mn><mo>=</mo><mn>0</mn></mtd></mtr><mtr><mtd><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>1</mn><mo>=</mo><mn>0</mn></mtd></mtr></mtable><mo>&#8660;</mo><mo>[</mo><mtable><mtr><mtd><mn>5</mn><mi>x</mi><mo>=</mo><mn>1</mn></mtd></mtr><mtr><mtd><mfenced><mrow><mi>x</mi><mo>-</mo><mn>1</mn></mrow></mfenced><mfenced><mrow><mi>x</mi><mo>+</mo><mn>1</mn></mrow></mfenced><mo>=</mo><mn>0</mn></mtd></mtr></mtable><mo>&#8660;</mo><mo>[</mo><mtable><mtr><mtd><mi>x</mi><mo>=</mo><mfrac><mn>1</mn><mn>5</mn></mfrac></mtd></mtr><mtr><mtd><mi>x</mi><mo>=</mo><mo>&#177;</mo><mn>1</mn></mtd></mtr></mtable></math></p> <p>Phương tr&igrave;nh c&oacute; ba nghiệm: <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>x</mi><mn>1</mn></msub><mo>=</mo><mfrac><mn>1</mn><mn>5</mn></mfrac><mo>,</mo><mo>&#160;</mo><msub><mi>x</mi><mn>2</mn></msub><mo>=</mo><mn>1</mn><mo>,</mo><mo>&#160;</mo><msub><mi>x</mi><mn>3</mn></msub><mo>=</mo><mo>-</mo><mn>1</mn></math>.</p>
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