lim(x->1)[ 1/(1-x) -3/(1-x^3) ]
=lim(x->1){ 1/(1-x) -3/[(1-x)(1+x+x^2)] }
=lim(x->1) [(1+x+x^2)-3]/[(1-x)(1+x+x^2)]
=lim(x->1)(x^2+x-2)/[(1-x)(1+x+x^2)] }
=lim(x->1)(x-1)(x+2)/[(1-x)(1+x+x^2)] }
=lim(x->1) -(x+2)/(1+x+x^2)
=-(1+2)/(1+1+1)
=-1
内容全部来源于网络收集，如有侵权，请联系网站删除：QQ：24596024