1)Tính
a) (4x + xy) (16x^2 - 8xy + 4y^2)
= (4x)^3 + (xy)^3
= 64x^3 + x^3y^3
b) (3/5xy + 2/3xz)(9/25x^2y^2 - 2/5x^2yz + 4/9x^2z^2)
= (3/5xy)^3 + (2/3xz)^3
= 27/125x^3y^3 + 8/27x^3z^3

2) Chứng minh
a) x^3 + y^3=(x+y). [(x-y)^2 + xy]
phân tích vế trái
x^3 + y^3
= (x + y)(x^2 - xy + y^2)
= (x + y)(x^2 - 2xy + y^2 + xy)
= (x + y)[(x^2 - 2xy + y^2) + xy]
= (x + y)[(x - y)^2 +xy]
= VP (đpcm)
b) x^3 + y^3 - xy(x+y) =(x+y) (x-y)^2
phân tích vế trái
x^3 + y^3 - xy(x + y)
= (x^3 + y^3) - xy(x + y)
= (x + y)(x^2 - xy + y^2) - xy(x + y)
= (x + y)(x^2 - xy + y^2 - xy)
= (x + y)(x^2 - 2xy + y^2)
= (x + y)(x - y)^2
= VP (đpcm)