数列an是等差数列,首项不为0,求lim(n*an/Sn)
人气：385 ℃ 时间：2020-02-04 22:52:31
解答
设等差为p
an=a1+(n-1)p
Sn=(a1+a1+(n-1)p)*n/2
lim(n*an/Sn)
=lim(n*(a1+(n-1)p)/((a1+a1+(n-1)p)*n/2)
=lim(2*(a1+(n-1)p)/(2a1+(n-1)p))
n趋向无穷时,n-1>>a1
所以等式趋向2
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