1楼最后算错了 引用一下：
1/(x+1) - 1/(x²-1) ÷ (x+1)/(x²-2x+1)
=1/(x+1) - 1/(x+1)(x-1) × (x-1)(x-1)/(x+1)
=1/(x+1) - (x-1)/(x+1)²
=[ (x+1)-(x-1) ] /(x+1)²
=2/(x+1)²