Rút gọn:

Rút gọn:
a) [(3x - 2)(x + 1) - (2x + 5)(x² - 1)] : (x + 1)
b) (2x + 1)² - 2(2x +1)(3 - x) + (3 - x)²
c) (x - 1)³ - (x + 1)(x² - x + 1) - (3x + 1)(1 - 3x)
d) (x + y + z - t)(x + y - z + t)