Hướng dẫn giải Bài 10 (Trang 8 SGK Toán Đại số 8, Tập 1)

Thực  hiện phép tính: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo> </mo><mfenced><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>2</mn><mi>x</mi><mo>+</mo><mn>3</mn></mrow></mfenced><mfenced><mrow><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>x</mi><mo>-</mo><mn>5</mn></mrow></mfenced></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo> </mo><mfenced><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>2</mn><mi>x</mi><mi>y</mi><mo>+</mo><msup><mi>y</mi><mn>2</mn></msup></mrow></mfenced><mfenced><mrow><mi>x</mi><mo>-</mo><mi>y</mi></mrow></mfenced></math> Giải: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo> </mo><mfenced><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>2</mn><mi>x</mi><mo>+</mo><mn>3</mn></mrow></mfenced><mfenced><mrow><mfrac><mn>1</mn><mn>2</mn></mfrac><mi>x</mi><mo>-</mo><mn>5</mn></mrow></mfenced><mspace linebreak="newline"/><mo>=</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><msup><mi>x</mi><mn>3</mn></msup><mo>-</mo><mn>5</mn><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>10</mn><mi>x</mi><mo>+</mo><mfrac><mn>3</mn><mn>2</mn></mfrac><mi>x</mi><mo>-</mo><mn>15</mn><mspace linebreak="newline"/><mo>=</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><msup><mi>x</mi><mn>3</mn></msup><mo>-</mo><mn>6</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mfrac><mn>23</mn><mn>2</mn></mfrac><mi>x</mi><mo>-</mo><mn>15</mn></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo> </mo><mfenced><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>2</mn><mi>x</mi><mi>y</mi><mo>+</mo><msup><mi>y</mi><mn>2</mn></msup></mrow></mfenced><mfenced><mrow><mi>x</mi><mo>-</mo><mi>y</mi></mrow></mfenced><mspace linebreak="newline"/><mo>=</mo><msup><mi>x</mi><mn>3</mn></msup><mo>-</mo><msup><mi>x</mi><mn>2</mn></msup><mi>y</mi><mo>-</mo><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mi>y</mi><mo>+</mo><mn>2</mn><mi>x</mi><msup><mi>y</mi><mn>2</mn></msup><mo>+</mo><mi>x</mi><msup><mi>y</mi><mn>2</mn></msup><mo>-</mo><msup><mi>y</mi><mn>3</mn></msup><mspace linebreak="newline"/><mo>=</mo><msup><mi>x</mi><mn>3</mn></msup><mo>-</mo><mn>3</mn><msup><mi>x</mi><mn>2</mn></msup><mi>y</mi><mo>+</mo><mn>3</mn><mi>x</mi><msup><mi>y</mi><mn>2</mn></msup><mo>-</mo><msup><mi>y</mi><mn>3</mn></msup></math>