定义:数列
对一切正整数
均满足
,称数列
为“凸数列”,以下关于 “凸数列”的说法:
①等差数列
一定是凸数列;
②首项
,公比
且
的等比数列
一定是凸数列;
③若数列
为凸数列,则数列
是单调递增数列;
④若数列
为凸数列,则下标成等差数列的项构成的子数列也为凸数列.
其中正确说法的序号是_________ .
![](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/e772be971634dc7230df59d91399dc59.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
①等差数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
②首项
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/390636a89883bd64bf8da9bf8654aff9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f71acdb04454c77e1e25ad4f336cccfe.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/45482d31d1d7448c9f3922b4d2a55331.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
③若数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d82c65a855b1eed9c43e6829f6c3bffb.png)
④若数列
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
其中正确说法的序号是
更新时间:2016-12-04 21:14:52
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【知识点】 数列的综合应用
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【推荐1】已知数列
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,对任意的
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是递增数列,
是递减数列,则数列
的通项公式为![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
_______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a8a03cd8f5930c737dc8877126a095f4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cea4ac187cbb465180e89f38250b3970.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bcf9491766bfabacaf5ab0bb508f6fa2.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/83cf38189d5cbf627d2b82ac0eb76006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3f7fda69e2b32b9ced2239f915fa59b.png)
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【推荐2】传说古希腊毕达哥拉斯学派的数学家经常在沙滩上画点或用小石子表示数.他们研究过如图所示的三角形数:
![](https://img.xkw.com/dksih/QBM/2019/4/8/2178030857281536/2178212774313984/STEM/3337a219767b4f4bbdbfb793f080b1d2.png?resizew=323)
将三角形数1,3,6,10,…记为数列
,将可被5整除的三角形数按从小到大的顺序组成一个新数列
,则①
是数列
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_______ (用k表示).
![](https://img.xkw.com/dksih/QBM/2019/4/8/2178030857281536/2178212774313984/STEM/3337a219767b4f4bbdbfb793f080b1d2.png?resizew=323)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/606e55241a2e145d54849129b8ffd20f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/039271f3111b0e21bc1282fcc22cf016.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fd18a8c008392f8bea248f710f665eec.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/606e55241a2e145d54849129b8ffd20f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/33d306d971f5ea762f9729df4e79b8ef.png)
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