A) (X - 1)(X2 - X + 1) = X3 - 1; B) (X3 + X2Y + XY2 + Y3)(X - Y) = X3 - Y3;

Bài 7. Chứng minh:

a) (x - 1)(x

²

- x + 1) = x

³

- 1;

b) (x

³

+ x

²

y + xy

²

+ y

³

)(x - y) = x

³

- y

³

;