问一道数学题化简求值题
问题描述：
问一道数学题化简求值题
先化简再求值（a- 2a/a+1 ）÷ a的平方-2a+1/a的平方-1 最后再 -a
a=5
答
[a- 2a/(a+1 ）]÷ (a²-2a+1)/(a²-1) -a
=a(a-1)/(a+1)÷ (a-1)²/(a+1)(a-1)-a
=a(a-1)/(a+1)÷ (a-1)/(a+1)-a
=a-a
=0