Bài 3: Phương trình bậc hai một ẩn
Hướng dẫn giải Bài 12 (Trang 42 SGK Toán Đại số 9, Tập 2)
<p><strong>12</strong>. Giải c&aacute;c phương tr&igrave;nh sau:</p> <p>a)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>8</mn><mo>=</mo><mn>0</mn></math>;</p> <p>b)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>5</mn><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>20</mn><mo>=</mo><mn>0</mn></math>;</p> <p>c)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mo>,</mo><mn>4</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>1</mn><mo>=</mo><mn>0</mn></math>;</p> <p>d)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><msqrt><mn>2</mn></msqrt><mi>x</mi><mo>=</mo><mn>0</mn></math>;</p> <p>e)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>-</mo><mn>0</mn><mo>,</mo><mn>4</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>1</mn><mo>,</mo><mn>2</mn><mi>x</mi><mo>=</mo><mn>0</mn></math>.</p> <p><strong>Giải:</strong>&nbsp;</p> <p>a)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>8</mn><mo>=</mo><mn>0</mn><mo>&#8660;</mo><msup><mi>x</mi><mn>2</mn></msup><mo>=</mo><mn>8</mn><mo>&#8660;</mo><mi>x</mi><mo>=</mo><mo>&#177;</mo><msqrt><mn>8</mn></msqrt><mo>&#8660;</mo><mi>x</mi><mo>=</mo><mo>&#177;</mo><mn>2</mn><msqrt><mn>2</mn></msqrt></math></p> <p>b)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>5</mn><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>20</mn><mo>=</mo><mn>0</mn><mo>&#8660;</mo><mn>5</mn><msup><mi>x</mi><mn>2</mn></msup><mo>=</mo><mn>20</mn><mo>&#8660;</mo><msup><mi>x</mi><mn>2</mn></msup><mo>=</mo><mn>4</mn><mo>&#8660;</mo><mi>x</mi><mo>=</mo><mo>&#177;</mo><mn>2</mn></math></p> <p>c)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn><mo>,</mo><mn>4</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>1</mn><mo>=</mo><mn>0</mn><mo>&#8660;</mo><mn>0</mn><mo>,</mo><mn>4</mn><msup><mi>x</mi><mn>2</mn></msup><mo>=</mo><mo>-</mo><mn>1</mn><mo>&#8660;</mo><msup><mi>x</mi><mn>2</mn></msup><mo>=</mo><mo>-</mo><mfrac><mn>10</mn><mn>4</mn></mfrac></math>: V&ocirc; nghiệm</p> <p>d)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><msqrt><mn>2</mn></msqrt><mi>x</mi><mo>=</mo><mn>0</mn><mo>&#8660;</mo><mi>x</mi><mo>(</mo><mn>2</mn><mi>x</mi><mo>+</mo><msqrt><mn>2</mn></msqrt><mo>)</mo><mo>=</mo><mn>0</mn><mo>&#8660;</mo><msqrt><mn>2</mn></msqrt><mi>x</mi><mo>(</mo><msqrt><mn>2</mn></msqrt><mi>x</mi><mo>+</mo><mn>1</mn><mo>)</mo><mo>=</mo><mn>0</mn><mo>&#160;</mo></math></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8660;</mo><mi>x</mi><mo>=</mo><mn>0</mn></math> hoặc&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mn>2</mn></msqrt><mi>x</mi><mo>+</mo><mn>1</mn><mo>=</mo><mn>0</mn></math><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8660;</mo><msub><mi>x</mi><mn>1</mn></msub><mo>=</mo><mn>0</mn></math> hoặc&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>x</mi><mn>2</mn></msub><mo>=</mo><mo>-</mo><mfrac><mn>1</mn><msqrt><mn>2</mn></msqrt></mfrac></math><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8660;</mo><msub><mi>x</mi><mn>1</mn></msub><mo>=</mo><mn>0</mn></math> hoặc&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>x</mi><mn>2</mn></msub><mo>=</mo><mo>-</mo><mfrac><msqrt><mn>2</mn></msqrt><mn>2</mn></mfrac></math></p> <p>e)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>-</mo><mn>0</mn><mo>,</mo><mn>4</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>1</mn><mo>,</mo><mn>2</mn><mi>x</mi><mo>=</mo><mn>0</mn><mo>&#8660;</mo><mo>-</mo><mn>4</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>12</mn><mi>x</mi><mo>=</mo><mn>0</mn><mo>&#8660;</mo><mo>-</mo><mn>4</mn><mi>x</mi><mo>(</mo><mi>x</mi><mo>-</mo><mn>3</mn><mo>)</mo><mo>=</mo><mn>0</mn><mo>&#8660;</mo><msub><mi>x</mi><mn>1</mn></msub><mo>=</mo><mn>0</mn></math> hoặc&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>x</mi><mn>2</mn></msub><mo>=</mo><mn>3</mn></math></p> <p>&nbsp;</p>
Hướng dẫn Giải Bài 12 (Trang 42, SGK Toán 9, Tập 2)
GV: GV colearn
Xem lời giải bài tập khác cùng bài
Video hướng dẫn giải bài tập
Hướng dẫn Giải Bài 12 (Trang 42, SGK Toán 9, Tập 2)
GV: GV colearn