Bài 3: Phương trình bậc hai một ẩn
Hướng dẫn giải Bài 11 (Trang 42 SGK Toán Đại số 9, Tập 2)
<p><strong>11.</strong> Đưa c&aacute;c phương tr&igrave;nh sau về dạng ax<sup>2&nbsp;</sup>+ bx + c = 0 v&agrave; chỉ r&otilde; c&aacute;c hệ số a, b, c :</p> <p>a)&nbsp;&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>5</mn><msup><mi>x</mi><mn>2</mn></msup><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>2</mn><mi>x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>4</mn><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mi>x</mi><mo>&#160;</mo><mo>;</mo></math></p> <p>b) <math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>3</mn><mn>5</mn></mfrac><msup><mi>x</mi><mrow><mn>2</mn><mo>&#160;</mo></mrow></msup><mo>+</mo><mo>&#160;</mo><mn>2</mn><mi>x</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>7</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>3</mn><mi>x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mo>&#160;</mo></math>;&nbsp;</p> <p>c)&nbsp;&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mi>x</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><msqrt><mn>3</mn></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mn>3</mn></msqrt><mi>x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>1</mn><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo></math>;</p> <p>d) <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><msup><mi>m</mi><mn>2</mn></msup><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>2</mn><mo>(</mo><mi>m</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>1</mn><mo>)</mo><mi>x</mi><mo>&#160;</mo><mo>,</mo><mo>&#160;</mo></math>m l&agrave; một hằng số&nbsp;</p> <p><strong>Giải&nbsp;</strong></p> <p>a)&nbsp; <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>5</mn><msup><mi>x</mi><mn>2</mn></msup><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>2</mn><mi>x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>4</mn><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mi>x</mi><mo>&#160;</mo><mo>&#8660;</mo><mo>&#160;</mo><mn>5</mn><msup><mi>x</mi><mn>2</mn></msup><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>3</mn><mi>x</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>4</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>&#160;</mo><mo>;</mo><mo>&#160;</mo><mi>a</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>5</mn><mo>,</mo><mo>&#160;</mo><mi>b</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>3</mn><mo>,</mo><mo>&#160;</mo><mi>c</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mo>-</mo><mn>4</mn></math></p> <p>b)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>3</mn><mn>5</mn></mfrac><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mo>&#160;</mo><mn>2</mn><mi>x</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>7</mn><mo>&#160;</mo><mo>=</mo><mn>3</mn><mi>x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><mo>&#8660;</mo><mfrac><mn>3</mn><mn>5</mn></mfrac><msup><mi>x</mi><mn>2</mn></msup><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mi>x</mi><mo>-</mo><mfrac><mn>15</mn><mn>2</mn></mfrac><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>&#160;</mo><mo>;</mo><mo>&#160;</mo><mi>a</mi><mo>=</mo><mfrac><mn>3</mn><mn>5</mn></mfrac><mo>,</mo><mo>&#160;</mo><mi>b</mi><mo>=</mo><mo>-</mo><mn>1</mn><mo>,</mo><mo>&#160;</mo><mi>c</mi><mo>=</mo><mo>-</mo><mfrac><mn>15</mn><mn>2</mn></mfrac></math></p> <p>c)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mo>&#160;</mo><mi>x</mi><mo>&#160;</mo><mo>-</mo><msqrt><mn>3</mn></msqrt><mo>=</mo><mo>&#160;</mo><msqrt><mn>3</mn></msqrt><mo>.</mo><mi>x</mi><mo>&#160;</mo><mo>+</mo><mn>1</mn><mo>&#160;</mo><mo>&#8660;</mo><mo>&#160;</mo><mo>&#160;</mo><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mo>&#160;</mo><mo>(</mo><mn>1</mn><mo>-</mo><mo>&#160;</mo><msqrt><mn>3</mn></msqrt><mo>)</mo><mi>x</mi><mo>&#160;</mo><mo>-</mo><mn>1</mn><mo>-</mo><msqrt><mn>3</mn></msqrt><mo>=</mo><mn>0</mn><mo>&#160;</mo><mo>&#160;</mo><mi>v</mi><mi>&#7899;</mi><mi>i</mi><mo>&#160;</mo><mi>a</mi><mo>=</mo><mn>2</mn><mo>,</mo><mo>&#160;</mo><mi>b</mi><mo>=</mo><mn>1</mn><mo>-</mo><msqrt><mn>3</mn></msqrt><mo>&#160;</mo><mo>,</mo><mi>c</mi><mo>=</mo><mo>&#160;</mo><mo>-</mo><mn>1</mn><mo>-</mo><msqrt><mn>3</mn></msqrt></math></p> <p>d) <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>2</mn><mo>(</mo><mi>m</mi><mo>-</mo><mn>1</mn><mo>)</mo><mi>x</mi><mo>&#160;</mo><mo>+</mo><msup><mi>m</mi><mn>2</mn></msup><mo>=</mo><mn>0</mn><mo>&#160;</mo><mo>;</mo><mo>&#160;</mo><mi>a</mi><mo>=</mo><mn>2</mn><mo>,</mo><mo>&#160;</mo><mi>b</mi><mo>=</mo><mo>-</mo><mn>2</mn><mo>(</mo><mi>m</mi><mo>-</mo><mn>1</mn><mo>)</mo><mo>,</mo><mo>&#160;</mo><mi>c</mi><mo>=</mo><mo>&#160;</mo><msup><mi>m</mi><mrow><mn>2</mn><mo>&#160;</mo></mrow></msup></math></p>
Hướng dẫn Giải Bài 11 (Trang 42, SGK Toán 9, Tập 2)
GV: GV colearn
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Hướng dẫn Giải Bài 11 (Trang 42, SGK Toán 9, Tập 2)
GV: GV colearn