Rút gọn biểu thức: a) (2x + 3y)^3 - (2x + 3y)(4x^2 - 6xy + 9y^2); b) (x^2 + 2)^2 - (x + 2)(x - 2)(x^2 + 4); c) (x - 1)^3 - 4x(x + 1)(x - 1) + 3(x - 1)(x^2 + x + 1)

Rút gọn biểu thức:
a) (2x + 3y)^3 - (2x + 3y)(4x^2 - 6xy + 9y^2)
b) (x^2 + 2)^2 - (x + 2)(x - 2)(x^2 + 4)
c) (x - 1)^3 - 4x(x + 1)(x - 1) + 3(x - 1)(x^2 + x + 1)
d) (x - 1)^3 + (x + 1)^3 + 6(x + 1)(x - 1)
_Tính:(a + b + c)^2 =