解题方法
1 . 已知等差数列
的前
项和为
,且
,
,有下列结论:
①
;②
;③
;④
.
其中正确的是______ .(填写所有正确结论的编号)
![](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/d0d47abde02e3d7ffb3484878ba43c19.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/db78d2181208520e31797e6538e1c6d8.png)
①
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e7a47513805617d84ad1e248c5415e5b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/42fa3df245bef16f30ef05302998bd39.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d8ee4c1f66f600c90d457a267aa0991.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/390636a89883bd64bf8da9bf8654aff9.png)
其中正确的是
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2 . 已知数列
满足葬
,仿照课本中推导等比数列前n项和公式的方法,可求得5Sn-4nan=_____
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://img.xkw.com/dksih/QBM/2016/10/17/1573072334340096/1573072340041728/STEM/755f23a16a3b47618537b0e68880c2d6.png?resizew=297)
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3 . 如果-1,a,b,c,-9成等比数列,那么b=_____
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