Khai triển a) (x + 3)^3; b) (x + 2y)^3.
Khai triển
a) (x + 3)3;
b) (x + 2y)3.
a) (x + 3)3 = x3 + 3 . x2 . 3 + 3 . x . 32 + 33 = x3 + 9x2 + 27x + 27;
b) (x + 2y)3 = x3 + 3 . x2 . 2y + 3 . x . (2y)2 + (2y)3
= x3 + 6x2y + 12xy2 + 8y3.