lim(3/(x^3-1)-1/(x-1),x趋于1,求极限

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lim(3/(x^3-1)-1/(x-1),x趋于1,求极限

lim(3/(x^3-1)-1/(x-1),x趋于1,求极限
lim(3/(x^3-1)-1/(x-1),x趋于1,求极限

lim(3/(x^3-1)-1/(x-1),x趋于1,求极限
lim [3/(x-1)(x²+x+1) -(x²+x+1)/(x-1)(x²+x+1)] x趋于1
=lim(3-x²-x-1)/(x-1)(x²+x+1) x趋于1
=lim -(x+2)(x-1)/(x²+x+1) x趋于1
=lim-(x+2)/(x²+x+1) x趋于1 用x=1代入
=-1

原式=lim[3/(x-1)(x²+x+1)-1/(x-1)]
=lim-(x-1)(x-2)/(x-1)(x²+x+1)
=lim(2-x)/(x²+x+1)
=1/3

解 limx→1{3/(x^3-1)-1/(x-1)}
=limx→1{3/[(x-1)(x²+x+1)]-1/(x-1)}通分得
=limx→1{(-x^2-x+2)/[(x-1)(x²+x+1)]}
=limx→1{-(x+2)/(x²+x+1)}
=-3/3
=-1