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