解：因为1/(1-x)-3/(1-x^3) =(1+x+x^2)/(1-x)(1+x+x^2)-3/(1-x)(1+x+x^2) =(x^2+x-2)/(1-x)(1+x+x^2) =(x+2)(x-1)/(1-x)(1+x+x^2) =-(x+2)/(1+x+x^2)把x=1代入即可lim (1/(1-x)-3/(1-x??)） x→1 =-1 是lim1/(1-x)-3/(1-x^3)吧?
lim1/(1-x)-3/(1-x^3) 通分得:
=lim(x^2+x+1-3)/(1-x^3)
=lim(x^2+x-2)/(1-x)(x^2+x+1)
=lim(x-1)(x+2)/(1-x)(x^2+x+1)
=-lim(x+2)/(x^2+x+1)
=-1
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