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问题: 求极限

limX->无穷大时:
N*[In(5+N)-InN]

解答:

n[ln(n+5)-lnn)]
=nln[(n+5)/n]
=nln(1+5/n)
=5*[n/5*ln(1+5/n)]
=5ln[(1+5/n)^(n/5)] n->∞,--->n/5->∞
所以n->+∞时,极限是5lne=5. (基本极限x->∞时lim(1+1/x)^x=e)
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