(m-n)3-(2n-m)3
＝﹙m－n－2n＋m﹚[﹙m－n﹚²＋﹙m－n﹚﹙2n－m﹚＋﹙2n－m﹚²]
＝﹙2m－3n﹚﹙m²－3mn＋3n²﹚我懂了谢谢立方差公式。a³－b³＝﹙a－b﹚﹙a²＋ab＋b²﹚