Tìm x biết: x^3 - x^2 - x + 1 = 0; (2x^3 - 3)^2 - (4x^2 - 9) = 0

Tìm x biết
a/ x^3 - x^2 - x + 1 = 0
b/ (2x^3 - 3)^2 - (4x^2 - 9) = 0
c/ x^4 + 2x^3 - 6x - 9 = 0
d/ 2(x + 5) - x^2 - 5x = 0