(3-a^2/a^2+2a+1)+｛1-（1/a+1)｝÷｛1+（1/a-1)｝
问题描述：
(3-a^2/a^2+2a+1)+｛1-（1/a+1)｝÷｛1+（1/a-1)｝
答
3-a^2/(a^2+2a+1)+(1-(1)/a+1)除以(1+(1)/a-1)
=3-a^2/(a^2+2a+1)+(a+1-1)/(a+1)除以(a-1+1)/(a-1)
=3-a^2/(a+1)^2+(a-1)/(a+1)
=[3-a²+（a+1)(a-1)]/(a+1)^2
=2/(a+1)^2