1) a(b + c) + 3(b + c) = (b + c)(a + 3)
2) y(a - c) + 5a - 5c = y(a - c) + 5(a - c) = (a - c)(y + 5
3) k(- a + b) - 2a + 2b = k(b - a) - 2(a - b) = k(b - a) + 2(b - a) = (b - a)(k + 2)
