求极限lim下面是x-->-1 [1/(x+1)-3/(x^3+1)]
问题描述：
求极限lim下面是x-->-1 [1/(x+1)-3/(x^3+1)]
答
先通分,然后用洛必塔法则
lim(x->-1) [1/(x+1)-3/(x^3+1)]
=lim(x->-1) [(x^2-x+1)/(x^3+1)-3/(x^3+1)]
=lim(x->-1) [(x^2-x-2)/(x^3+1)]
=lim(x->-1) [(2x-1)/(3x^2)]
=-1