20-21高二·全国·课后作业
解题方法
1 . (1)已知等差数列
的前n项和为
,则
成等差数列吗?证明你的结论;
(2)已知等比数列
的前n项的和为
,则
成等比数列吗?证明你的结论.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3097007589d479d0f47f15823c6dcbc6.png)
(2)已知等比数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08eb71ecf8d733b6932f4680874dbbf3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3097007589d479d0f47f15823c6dcbc6.png)
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