是因式分解吧?ab﹙c²－d²﹚＋cd﹙a²－b²﹚原式＝abc²－abd²＋cda²－cdb²＝﹙abc²＋cda²﹚－﹙abd²＋cdb²﹚＝ac﹙bc＋ad﹚－bd﹙bc＋ad﹚＝﹙ac－bd﹚...