[（b-3a）^2]^﹙n+1﹚*[﹙3a-b﹚^2n+1]^3
=[（3a-b）^2]^﹙n+1﹚*[﹙3a-b﹚^2n+1]^3
=（3a-b）^2﹙n+1﹚*﹙3a-b﹚^3(2n+1)
=（3a-b）^(7n+5﹚