x³＋y³
=﹙x＋y﹚﹙x²－xy＋y²﹚
=﹙x＋y﹚﹙x²＋2xy＋y²－xy﹚
=1×[﹙x＋y﹚²－xy]
=1²－﹙－1﹚
=2