（1-2）^2 / X-1
问题描述：
（1-2）^2 / X-1
— —
X+1 X+1
..
就是 （1- X+1分之2）的平方除以X+1分之X-1
答
[1-2/(x+1)]^2÷(x-1)/(x+1)
=[1-2/(x+1)]^2*(x+1)/(x-1)
=[(x+1-2)/(x+1)]^2*(x+1)/(x-1)
=[(x-1)/(x+1)]^2*(x+1)/(x-1)
=(x-1)^2/(x+1)^2*(x+1)/(x-1)
=(x-1)/(x+1)