13 Efectuați: a (x-2)(x + 2)(x² + 4) - (x² + 1)² + 2(x + 1)²; b (x+4) (x² − 3) − x(x + 2)² + (x - 1)²; c (x² + 2) (x² −5) − x²(x + 1)² + 2x(x - 1)²; d (2xy²-7)(2xy² + 7) - (2xy² - 1)²; e (5x-7)-[2(x + 2) + 3(x+1)] − (4x-3) - [3(x+3)+x-6]; f (x + 1) - [5(x + 1) - 2(x + 4)] - (3x + 2) [7(x + 2) - 4(x+3)].
va rog sa ma ajutati!​