求x趋于1,lim(x+x^2+……+x^n-n)/(x-1)的极限,

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求x趋于1,lim(x+x^2+……+x^n-n)/(x-1)的极限,
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求x趋于1,lim(x+x^2+……+x^n-n)/(x-1)的极限,
求x趋于1,lim(x+x^2+……+x^n-n)/(x-1)的极限,

求x趋于1,lim(x+x^2+……+x^n-n)/(x-1)的极限,
x^k-1=(x-1)[x^(k-1)+x^(k-2)+……+x+1]
x+x^2+……+x^n-n
=(x-1)+(x^2-1)+……+(x^n-1)
=(x-1)[1+(x+1)+……+(x^(n-1)+x^(n-2)+……+x+1)]
所以
lim(x→1) (x+x^2+……+x^n-n)/(x-1)
=lim(x→1) [1+(x+1)+……+(x^(n-1)+x^(n-2)+……+x+1)]
=1+2+……+n
=n(n+1)/2