Tìm x biết: (x + 2)(x^2 - 2x + 4) - x(x^2 + 2) = 15

Tìm x, biết
a) (x + 2)(x2 - 2x + 4)- x(x2 + 2) = 15;
b) (x + 3) - x(3x + 1)2 + (2x + 1)(4x2- 2x + 1) = 28
c) (x – 1) - (x' + x2 + 1)(x2 - 1) = 0.