已知等比数列{an}为6,3,3/2,.,它的前n项和为Sn,求使得Sn大于23/2的n的最小值

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已知等比数列{an}为6,3,3/2,.,它的前n项和为Sn,求使得Sn大于23/2的n的最小值
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此等比数列首项为6,公比为q=3/6=1/2,
∴Sn
=6[1-(1/2)^n]/[1-(1/2)]
=12-3*(1/2)^(n-2)
当Sn>23/2时,有
2^(n-3)>3,
∴n-3>log(2,3),[指以2为底,3的对数]
∴n>3+log(2,3)
∵1=log(2,2)

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