(1/a+3)-(6/9-a的平方)=?
问题描述：
(1/a+3)-(6/9-a的平方)=?
答
1/(a+3)-6/(9-a²)
=1/(a+3)+6/(a²-9)
=1/(a+3)+6/[(a+3)(a-3)]
=(a-3)/[(a+3)(a-3)]+6/[(a+3)(a-3)]
=(a+3)/[(a+3)(a-3)]
=1/(a-3)