3/(a+1)-12/(a²-1)-6/(1-a)

问题描述:

3/(a+1)-12/(a²-1)-6/(1-a)

3/﹙a+1﹚-12/﹙a²-1﹚-6/﹙1-a﹚
=﹙3a-3﹚/﹙a²-1﹚-12/﹙a²-1﹚+﹙6a+6﹚/﹙a²-1﹚
=﹙3a-3-12+6a+6﹚/﹙a²-1﹚
=9﹙a-1﹚/﹙a²-1﹚
=9/﹙a+1﹚.