c) (x + y)(x^2 + 2xy + y^2);
Giải thích
c) (x + y)(x2 + 2xy + y2)
= x . x2 + x . 2xy + x . y2 + y . x2 + y . 2xy + y . y2
= x3 + 2x2y + xy2 + x2y + 2xy2 + y3
= x3 + (2x2y + x2y) + (xy2 + 2xy2) + y3
= x3 + 3x2y + 3xy2 + y3.
c) (x + y)(x2 + 2xy + y2)
= x . x2 + x . 2xy + x . y2 + y . x2 + y . 2xy + y . y2
= x3 + 2x2y + xy2 + x2y + 2xy2 + y3
= x3 + (2x2y + x2y) + (xy2 + 2xy2) + y3
= x3 + 3x2y + 3xy2 + y3.