soluzione Scomporre     (x - 3y)4 - (2x - y)4 = = [(x - 3y)2 - (2x - y)2] [(x - 3y)2 + (2x - y)2] = = [(x - 3y) - (2x - y) ] [(x - 3y) + (2x - y)] [(x - 3y)2 + (2x - y)2] = = (-x - 2y) (3x - 4y) (x2 - 6xy +9y2 + 4x2 -4xy + y2) = = -(x + 2y) (3x - 4y) (5x2 -10xy +10y2) = = -5 (x + 2y) (3x - 4y) (x2 -2xy + 2y2)