lim [1/(1-x)-3/(1-x^3)] 这样?拜托把括号加对 囧
=lim (1+x+x^2-3)/(1-x^3) 通分
=lim (x^2+x-2)/(1-x^3)
=lim (x-1)(x+2)/(1-x^3)
=-lim (x+2)/(1+x+x^2)
=-3/3
=-1