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