1-m²－n²＋2mn
=1-(m-n)²
=﹙1+m-n)(1-m+n)
4x²－y²＋2x－y
=﹙2x＋y﹚﹙2x－y﹚＋﹙2x－y﹚
=﹙2x－y﹚﹙2x＋y＋1﹚