(1)化简（1+1/a-1)(1/a的平方-1）=a/(a-1)×1/(a-1)(a+1)=a/(a-1)²(a+1)取a=2,有意义（a+1/a-1+1/a的平方-2a+1）÷a/a-1=[(a+1)/(a-1)+1/(a-1)²]×(a-1)/a=[a²/(a-1)²]×(a-1)/a=a/(a-1)取a=2有意义。
