18. Efectuați calculele:
a) (x + 2)(x² – x + 3) - (x + 1)(x2 + 2x - 5);
b) (2x + 1)(x² – 2x + 4) - (x – 3)(2x² + x + 3);
c) (x – 3)(x2 – 3x + 2) - (x + 3)(x² – 2x + 3);
d) (2x - 1)(-x2 + x - 2) + (2x - 3)(x² - x + 1).
Dau coroană​