1, ab + ac = a(b + c)
2, ab - ac + ad = a(b - c + d)
3, ax - bx - cx + dx = x(a - b - c + d)
4, a(b + c) - d(b + c) = (a - d)(b + c)
5, ac - ad + bc - bd = a(c - d) + b(c - d)
= (a + b)(c - d)
6, ax + by + bx + ay = a(x + y) + b(x + y)
= (a + b)(x + y)