先化简 再求值 x^2-1/x^2-2x+1÷x+1/x-1×1-x/1+x
问题描述：
先化简 再求值 x^2-1/x^2-2x+1÷x+1/x-1×1-x/1+x
答
=(x+1)(x-1)/(x-1)² ×(x-1)/(x+1) ×(1-x)/(1+x)
=(x+1)/(x-1) ×(x-1)/(x+1) ×(1-x)/(1+x)
=(1-x)/(1+x)����x=1/2��x=1/2ʱԭʽ=(1-1/2)/(1+1/2) =1/3