(a的平方-2a+1)/( a-1)+(a-a的三次方)/(a+1)
=（a-1)²/(a-1)-a(a-1)(a+1)/(a+1)
=a-1-a(a-1)
=a-1-a²+a
=-a²+2a-1 a=1
=-(a-1)²
=-(1-1)²
=0确定是对的吗？不是=-a²-1确定是对的