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等比数列求和公式推导

更新时间： 2021-02-08 08:24:25

1、等比数列Sn=a1×(1-q^n)/(1-q)，Sn=n×a1（当q=1时）。

2、推导过程为：q×Sn=a1×q+a2×q+…+an×q=a2+a3+…+a(n+1)，Sn-q×Sn=a1-a(n+1)=a1-a1×q^n，(1-q)×Sn=a1×(1-q^n)。

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