Răspuns:
a) (x + 1)(x - 5) + (x + 1) = (x + 1)(x - 5 + 1) = (x + 1)(x - 4)
b) (x-2)(x+3) -2(x + 3) = (x + 3)(x - 2 - 2) = (x + 3)(x - 4)
c)(x-4)(x + 6)-3(x - 4) = (x - 4)(x + 6 - 3) = (x - 4)(x + 3)
d) (x + 5)(x + 7) + 6(x + 7) = (x + 7)(x + 5 + 6) = (x + 7)(x + 11)