Hướng dẫn Giải Bài 35 (trang 20, SGK Toán 9, Tập 1)

Hướng dẫn giải Bài 35 (Trang 20 SGK Toán 9, Tập 1)

Bài 35 (Trang 20 SGK Toán 9, Tập 1): Tìm x, biết: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">a</mi><mo>)</mo><mo> </mo><msqrt><msup><mfenced><mrow><mi mathvariant="normal">x</mi><mo>-</mo><mn>3</mn></mrow></mfenced><mn>2</mn></msup></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>9</mn><mo>;</mo></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo> </mo><msqrt><mn>4</mn><msup><mi>x</mi><mn>2</mn></msup><mo> </mo><mo>+</mo><mo> </mo><mn>4</mn><mi>x</mi><mo> </mo><mo>+</mo><mo> </mo><mn>1</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>6</mn><mo>.</mo></math>   Hướng dẫn giải: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">a</mi><mo>)</mo><mo> </mo><msqrt><msup><mfenced><mrow><mi mathvariant="normal">x</mi><mo>-</mo><mn>3</mn></mrow></mfenced><mn>2</mn></msup></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>9</mn><mspace linebreak="newline"/><mo>⇔</mo><mfenced open="|" close="|"><mrow><mi>x</mi><mo> </mo><mo>-</mo><mo> </mo><mn>3</mn></mrow></mfenced><mo> </mo><mo>=</mo><mo> </mo><mn>9</mn><mspace linebreak="newline"/><mo>⇔</mo><mi>x</mi><mo> </mo><mo>-</mo><mo> </mo><mn>3</mn><mo> </mo><mo>=</mo><mo> </mo><mn>9</mn><mo> </mo><mi>h</mi><mi>o</mi><mi>ặ</mi><mi>c</mi><mo> </mo><mi>x</mi><mo> </mo><mo>-</mo><mo> </mo><mn>3</mn><mo> </mo><mo>=</mo><mo> </mo><mo>-</mo><mn>9</mn><mspace linebreak="newline"/><mo>⇔</mo><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><mn>12</mn><mo> </mo><mi>h</mi><mi>o</mi><mi>ặ</mi><mi>c</mi><mo> </mo><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><mo>-</mo><mn>6</mn></math> Vậy phương trình đã cho có hai nghiệm là x = 12 và x = -6. <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo> </mo><msqrt><mn>4</mn><msup><mi>x</mi><mn>2</mn></msup><mo> </mo><mo>+</mo><mo> </mo><mn>4</mn><mi>x</mi><mo> </mo><mo>+</mo><mo> </mo><mn>1</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>6</mn><mspace linebreak="newline"/><mo>⇔</mo><msqrt><msup><mn>2</mn><mn>2</mn></msup><msup><mi>x</mi><mn>2</mn></msup><mo> </mo><mo>+</mo><mo> </mo><mn>4</mn><mi>x</mi><mo> </mo><mo>+</mo><mo> </mo><mn>1</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>6</mn><mspace linebreak="newline"/><mo>⇔</mo><msqrt><msup><mfenced><mrow><mn>2</mn><mi>x</mi></mrow></mfenced><mn>2</mn></msup><mo> </mo><mo>+</mo><mo> </mo><mn>2</mn><mo>.</mo><mn>2</mn><mi>x</mi><mo> </mo><mo>+</mo><mo> </mo><msup><mn>1</mn><mn>2</mn></msup></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>6</mn><mspace linebreak="newline"/><mo>⇔</mo><msqrt><msup><mfenced><mrow><mn>2</mn><mi>x</mi><mo> </mo><mo>+</mo><mo> </mo><mn>1</mn></mrow></mfenced><mn>2</mn></msup></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>6</mn><mspace linebreak="newline"/><mo>⇔</mo><mn>2</mn><mi>x</mi><mo> </mo><mo>+</mo><mo> </mo><mn>1</mn><mo> </mo><mo>=</mo><mo> </mo><mn>6</mn><mo> </mo><mi>h</mi><mi>o</mi><mi>ặ</mi><mi>c</mi><mo> </mo><mn>2</mn><mi>x</mi><mo> </mo><mo>+</mo><mo> </mo><mn>1</mn><mo> </mo><mo>=</mo><mo> </mo><mo>-</mo><mn>6</mn><mspace linebreak="newline"/><mo>⇔</mo><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><mfrac><mn>5</mn><mn>2</mn></mfrac><mo> </mo><mi>h</mi><mi>o</mi><mi>ặ</mi><mi>c</mi><mo> </mo><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mo>-</mo><mn>7</mn></mrow><mn>2</mn></mfrac></math> Vậy phương trình đã cho có 2 nghiệm là <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><mfrac><mn>5</mn><mn>2</mn></mfrac></math> và <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mo>-</mo><mn>7</mn></mrow><mn>2</mn></mfrac></math>.