Hướng dẫn Giải Bài 33 (trang 19, SGK Toán 9, Tập 1)

Hướng dẫn giải Bài 33 (Trang 19 SGK Toán 9, Tập 1)

Bài 33 (Trang 19 SGK Toán 9, Tập 1): Giải phương trình: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">a</mi><mo>)</mo><mo> </mo><msqrt><mn>2</mn></msqrt><mo>.</mo><mi mathvariant="normal">x</mi><mo> </mo><mo>-</mo><mo> </mo><msqrt><mn>50</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>0</mn><mo>;</mo></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">b</mi><mo>)</mo><mo> </mo><msqrt><mn>3</mn></msqrt><mo>.</mo><mi mathvariant="normal">x</mi><mo> </mo><mo>+</mo><msqrt><mn>3</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>12</mn></msqrt><mo> </mo><mo>+</mo><mo> </mo><msqrt><mn>27</mn></msqrt><mo>;</mo></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">c</mi><mo>)</mo><mo> </mo><msqrt><mn>3</mn></msqrt><mo>.</mo><msup><mi mathvariant="normal">x</mi><mn>2</mn></msup><mo> </mo><mo>-</mo><mo> </mo><msqrt><mn>12</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>0</mn><mo>;</mo></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">d</mi><mo>)</mo><mo> </mo><mfrac><msup><mi mathvariant="normal">x</mi><mn>2</mn></msup><msqrt><mn>5</mn></msqrt></mfrac><mo> </mo><mo>-</mo><mo> </mo><msqrt><mn>20</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>0</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><mn>2</mn></msqrt><mo>.</mo><mi mathvariant="normal">x</mi><mo> </mo><mo>-</mo><mo> </mo><msqrt><mn>50</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>0</mn><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msqrt><mn>2</mn></msqrt><mi mathvariant="normal">x</mi><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>50</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><mi mathvariant="normal">x</mi><mo> </mo><mo>=</mo><mo> </mo><msqrt><mfrac><mn>50</mn><mn>2</mn></mfrac></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><mi mathvariant="normal">x</mi><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>25</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><mi mathvariant="normal">x</mi><mo> </mo><mo>=</mo><mo> </mo><mn>5</mn></math> Vậy x = 5.   <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">b</mi><mo>)</mo><mo> </mo><msqrt><mn>3</mn></msqrt><mo>.</mo><mi mathvariant="normal">x</mi><mo> </mo><mo>+</mo><msqrt><mn>3</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>12</mn></msqrt><mo> </mo><mo>+</mo><mo> </mo><msqrt><mn>27</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msqrt><mn>3</mn></msqrt><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>12</mn></msqrt><mo> </mo><mo>+</mo><mo> </mo><msqrt><mn>27</mn></msqrt><mo> </mo><mo>-</mo><mo> </mo><msqrt><mn>3</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msqrt><mn>3</mn></msqrt><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>4</mn><mo>.</mo><mn>3</mn></msqrt><mo> </mo><mo>+</mo><mo> </mo><msqrt><mn>9</mn><mo>.</mo><mn>3</mn></msqrt><mo> </mo><mo>-</mo><mo> </mo><msqrt><mn>3</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msqrt><mn>3</mn></msqrt><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><mn>2</mn><msqrt><mn>3</mn></msqrt><mo> </mo><mo>+</mo><mo> </mo><mn>3</mn><msqrt><mn>3</mn></msqrt><mo> </mo><mo>-</mo><mo> </mo><msqrt><mn>3</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><mn>2</mn><mo> </mo><mo>+</mo><mo> </mo><mn>3</mn><mo> </mo><mo>-</mo><mo> </mo><mn>1</mn><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><mi>x</mi><mo> </mo><mo>=</mo><mo> </mo><mn>4</mn></math> Vậy x = 4.   <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">c</mi><mo>)</mo><mo> </mo><msqrt><mn>3</mn></msqrt><mo>.</mo><msup><mi mathvariant="normal">x</mi><mn>2</mn></msup><mo> </mo><mo>-</mo><mo> </mo><msqrt><mn>12</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>0</mn><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msqrt><mn>3</mn></msqrt><msup><mi mathvariant="normal">x</mi><mn>2</mn></msup><mo> </mo><mo>-</mo><mo> </mo><msqrt><mn>12</mn></msqrt><mo> </mo><mo>=</mo><mo> </mo><mn>0</mn><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msqrt><mn>3</mn></msqrt><msup><mi mathvariant="normal">x</mi><mn>2</mn></msup><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>4</mn><mo>.</mo><mn>3</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msqrt><mn>3</mn></msqrt><msup><mi mathvariant="normal">x</mi><mn>2</mn></msup><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>4</mn></msqrt><mo>.</mo><msqrt><mn>3</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msup><mi mathvariant="normal">x</mi><mn>2</mn></msup><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>4</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msup><mi mathvariant="normal">x</mi><mn>2</mn></msup><mo> </mo><mo>=</mo><mo> </mo><mn>2</mn><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><msqrt><msup><mi mathvariant="normal">x</mi><mn>2</mn></msup></msqrt><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>2</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><mfenced open="|" close="|"><mi mathvariant="normal">x</mi></mfenced><mo> </mo><mo>=</mo><mo> </mo><msqrt><mn>2</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>⇔</mo><mo> </mo><mi mathvariant="normal">x</mi><mo> </mo><mo>=</mo><mo> </mo><mo>±</mo><msqrt><mn>2</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mi>Vậy</mi><mo> </mo><mi mathvariant="normal">x</mi><mo> </mo><mo>=</mo><mo> </mo><mo>±</mo><msqrt><mn>2</mn></msqrt></math>