设等比数列{an}的前n项和为Sn,若S10=40,S20=120,则S30=_____ .
更新时间:2017-09-23 15:27:29
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【知识点】 等比数列前n项和的性质
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【推荐1】已知
是正项等比数列
的前n项和,
,则
的最小值为______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1cb1b127b6207bf1958b9cb6b999daa0.png)
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【推荐2】设
是等比数列
的前
项和,若
,
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/130aab74cff7810ad14ac2480ff5b929.png)
_________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c705ed1d40eb3d40ebadd05dbb645b73.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dc737fd79335e429f265108d8dd2504c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/130aab74cff7810ad14ac2480ff5b929.png)
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