Hướng dẫn giải Bài 18 (Trang 11 SGK Toán Đại số 8, Tập 1)

Hãy tìm cách giúp bạn An khôi phục lại những hằng đẳng thức bị mực làm nhòe đi một số chỗ: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo> </mo><msup><mi>x</mi><mn>2</mn></msup><mo> </mo><mo>+</mo><mo> </mo><mn>6</mn><mi>x</mi><mi>y</mi><mo> </mo><mo>+</mo><mo> </mo><mo>…</mo><mo> </mo><mo>=</mo><mo> </mo><msup><mrow><mo>(</mo><mo>…</mo><mo> </mo><mo>+</mo><mo> </mo><mn>3</mn><mi>y</mi><mo>)</mo></mrow><mn>2</mn></msup><mo>;</mo></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo> </mo><mo>.</mo><mo>.</mo><mo>.</mo><mo> </mo><mo>–</mo><mo> </mo><mn>10</mn><mi>x</mi><mi>y</mi><mo> </mo><mo>+</mo><mo> </mo><mn>25</mn><msup><mi>y</mi><mn>2</mn></msup><mo> </mo><mo>=</mo><mo> </mo><msup><mrow><mo>(</mo><mo>…</mo><mo> </mo><mo>-</mo><mo> </mo><mo>…</mo><mo>)</mo></mrow><mn>2</mn></msup><mo>;</mo></math> Hãy nêu một số đề bài tương tự Giải: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo> </mo><msup><mi>x</mi><mn>2</mn></msup><mo> </mo><mo>+</mo><mn>2</mn><mo>.</mo><mi>x</mi><mo>.</mo><mn>3</mn><mi>y</mi><mo>+</mo><mo>.</mo><mo>.</mo><mo>.</mo><mo>=</mo><msup><mfenced><mrow><mo>.</mo><mo>.</mo><mo>.</mo><mo>+</mo><mn>3</mn><mi>y</mi></mrow></mfenced><mn>2</mn></msup><mspace linebreak="newline"/><msup><mi>x</mi><mn>2</mn></msup><mo> </mo><mo>+</mo><mn>2</mn><mo>.</mo><mi>x</mi><mo>.</mo><mn>3</mn><mi>y</mi><mo>+</mo><msup><mfenced><mrow><mn>3</mn><mi>y</mi></mrow></mfenced><mn>2</mn></msup><mo>=</mo><msup><mfenced><mrow><mi>x</mi><mo>+</mo><mn>3</mn><mi>y</mi></mrow></mfenced><mn>2</mn></msup><mspace linebreak="newline"/><mi>V</mi><mi>ậ</mi><mi>y</mi><mo>:</mo><msup><mi>x</mi><mn>2</mn></msup><mo> </mo><mo>+</mo><mn>6</mn><mi>x</mi><mi>y</mi><mo>+</mo><mn>9</mn><msup><mi>y</mi><mn>2</mn></msup><mo>=</mo><msup><mfenced><mrow><mi>x</mi><mo>+</mo><mn>3</mn><mi>y</mi></mrow></mfenced><mn>2</mn></msup></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo> </mo><mo>.</mo><mo>.</mo><mo>.</mo><mo>-</mo><mn>2</mn><mo>.</mo><mi>x</mi><mo>.</mo><mn>5</mn><mi>y</mi><mo>+</mo><msup><mfenced><mrow><mn>5</mn><mi>y</mi></mrow></mfenced><mn>2</mn></msup><mo>=</mo><msup><mfenced><mrow><mo>.</mo><mo>.</mo><mo>.</mo><mo>-</mo><mo>.</mo><mo>.</mo><mo>.</mo></mrow></mfenced><mn>2</mn></msup><mo>;</mo><mspace linebreak="newline"/><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>2</mn><mo>.</mo><mi>x</mi><mo>.</mo><mn>5</mn><mi>y</mi><mo>+</mo><msup><mfenced><mrow><mn>5</mn><mi>y</mi></mrow></mfenced><mn>2</mn></msup><mo>=</mo><msup><mfenced><mrow><mi>x</mi><mo>-</mo><mn>5</mn><mi>y</mi></mrow></mfenced><mn>2</mn></msup><mspace linebreak="newline"/><mi>V</mi><mi>ậ</mi><mi>y</mi><mo>:</mo><mo> </mo><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>10</mn><mi>x</mi><mi>y</mi><mo>+</mo><mn>25</mn><msup><mi>y</mi><mn>2</mn></msup><mo>=</mo><msup><mfenced><mrow><mi>x</mi><mo>-</mo><mn>5</mn><mi>y</mi></mrow></mfenced><mn>2</mn></msup></math> Đề bài tương tự: Chẳng hạn: <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>4</mn><mi>x</mi><mo> </mo><mo>+</mo><mo> </mo><mn>4</mn><mi>x</mi><mi>y</mi><mo> </mo><mo>+</mo><mo> </mo><mo>…</mo><mo> </mo><mo>=</mo><mo> </mo><mo>(</mo><mo>…</mo><mo> </mo><mo>+</mo><mo> </mo><msup><mi>y</mi><mn>2</mn></msup><mo>)</mo></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>…</mo><mo> </mo><mo>-</mo><mo> </mo><mn>8</mn><mi>x</mi><mi>y</mi><mo> </mo><mo>+</mo><mo> </mo><msup><mi>y</mi><mn>2</mn></msup><mo>=</mo><mo> </mo><msup><mrow><mo>(</mo><mo>…</mo><mo> </mo><mo>-</mo><mo> </mo><mo>…</mo><mo>)</mo></mrow><mn>2</mn></msup></math>