Thực hiện phép tính (x)(x - y) - (x + 1)(x + ỹ) + (y)(x - xy^2)

Ta có: xx−y−x+1x+yx+yx−xy2

                  =x.x−y.x−x.x+1+yx.x+1+x.y−xy2.y

                  =x2−xy−x2+x+yx2+xy+xy−xy3

                  =x2−xy−x2−x−yx2−xy+xy−xy3

                  =−xy−x−yx2−xy3