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11. Calculează: a) (x+2y) (r² - 2xy + 4y²) - 8y³; b) (x − 2) (x³ + 2x² + 4x + 8) - (x − 2)(x + 2) (x² + 4); c) (x − 3)(x-2) + (x+4) (x-1)- (2x - 1)(x - 2); d) (x - 5) (x + 2) - 2 (x-1) (x+3)+x².​