原式=(x-1)²/(x+1)(x-1)*(x+1)/x(x-1)-1/x+1=1/x-1/x+1=1即不论x取何值，结果都是1所以x错了也一样
x²-1分之x²-2x+1÷x+1分之x²-x -x分之1+1=[(x-1)²/(x+1)(x-1)]×[(x+1)/x(x-1)]-1/x+1=1/x-1/x+1=1
