(a-1)/(a²+2a+1)=(a-1)/(a+1)²,
1/(a²-1)=1/[(a+1)(a-1)],
公分母：(a+1)²(a-1),
题目不全,无法通分,但已经有了公分母,通分就简单了.a²+2a+1分之a-1，a²-1分之6. …………通分刚漏打了- -不好意思哈公分母：(a+1)²(a-1),(a-1)/(a²+2a+1)=(a-1)/(a+1)²=(a-1)^2/[(a+1)²(a-1)]6/(a²-1)=6/[(a+1)(a-1)]=6(a+1)/[(a+1)²(a-1)]。