③﹙x＋y﹚﹙x－1﹚－xy－xy²
=x²-x-y+xy－xy－xy²
=x²-x-y-xy²
④x³﹙x－y﹚＋4x﹙y－x﹚
=（x³-4x）﹙x－y﹚
=x（x-2）（x+2）﹙x－y﹚