Hoặc
b) x2y2−12xy+2x−2y.
b) x2y2−12xy+2x−2y
=x2y2.x−12xy.x+2x−x2y2.2y+12xy.2y−2.2y
=x3y2−12x2y+2x−2x2y3+xy2−4y.