1 . 已知等差数列
的前
项和为
,且
,
,若将
去掉一项后,剩下三项依次为等比数列
的前三项,则
为__________ .
![](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/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81911c0e1a8b5472bbec7b78974f5bf2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d55f82fc5641af25aaf2533015d4273e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5ed6fe44bc49b478979589face327799.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/034ba25825c13725931c483aa47c9363.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a548938d87c80ac47910607d3857007f.png)
您最近一年使用:0次
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解题方法
2 . 已知正项等差数列
的前
项和为
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/13f0c7910375313c173f0810dca0e500.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/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/13f0c7910375313c173f0810dca0e500.png)
您最近一年使用:0次