soluzione Calcolare x - 2 x + 2     + x   = x + 3 x - 3 = x - 2 x + 2 · x + 3 x - 3 + x = = (x - 2)(x + 3) (x + 2)(x - 3) + x = = (x - 2)(x + 3) +x(x + 2)(x - 3) (x + 2)(x - 3) = = x2 + x - 6 + x3 - x2 + 6x (x + 2)(x - 3) = = x3 + 7x - 6 (x + 2)(x - 3)