求[ n^2(k/n-1/(n+1)-1/(n+2)- .-1/(k+1)] 的极限的值

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求[ n^2(k/n-1/(n+1)-1/(n+2)- .-1/(k+1)] 的极限的值

可以把k/n看作1/n+1/n+1/n.一共k个1/n(k*(1/n))
则原式=n^2(1/n-1/(n+1)+1/n-1/(n+2)+.+1/n-1/(k+1))
=n^2(1/n(n-1)+2/n(n-1)+.+k/n(n-1))
=n/(n-1)+2n/(n-1).kn/(n-1)
lim[n/(n-1)+2n/(n-1).kn/(n-1)]=k(k+1)/2