1) аb + 2b - 2a - 4 = b(a + 2) - 2(a + 2) = (b - 2)(a + 2)
2) x^2 + xy + ax + ay = x(x + y) + a(x + y) = (x + a)(x + y)
3) am - an + m - n = a(m - n) + 1(m - n) = (a + 1)(m - n)
4) 3x - 3y + ax - ay = 3(x - y) + a(x - y) = (3 + a)(x - y)
5) ab - a^2 + 2a - 2b = a(b - a) - 2(b - a) = (a - 2)(b - a)