题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073020-61791.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073020-44425.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073020-32336.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073021-22868.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073020-44425.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073020-32336.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073021-41361.png)
A.![]() | B.![]() | C.![]() | D.![]() |
答案
解析
分析:由题意可知5×a
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073022-59815.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073022-81386.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073022-53454.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073023-34652.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073023-42432.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073023-34652.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073023-24001.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073023-45296.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073021-54398.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073024-51897.png)
解答:解:∵S
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073022-53454.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073022-59815.png)
∴an2+ ≥λa12可以转化为5×a
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073022-59815.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073022-81386.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073022-53454.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073023-34652.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073023-42432.png)
两边除以a12,设 x=
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073024-81919.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073024-26949.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073024-51897.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073024-62217.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073025-71722.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073024-26949.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073021-54398.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073024-51897.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073021-54398.png)
∴当 x=-
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073021-54398.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073021-54398.png)
点评:本题考查数列的性质和应用,解题时要认真审题,注意挖掘隐含条件.
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073006-50100.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073006-47609.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073006-69035.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073006-50100.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073006-36748.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073006-20346.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073007-62199.jpg)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013073007-74280.jpg)
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072955-46845.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072955-99365.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072955-61028.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072955-23175.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072955-80855.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072956-54144.gif)
(1)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072955-46845.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072956-54144.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072956-23441.gif)
(3)记数列
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072956-81626.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072955-99365.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072956-79659.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072957-30158.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072957-43015.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072941-60806.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072941-55434.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072942-33365.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072941-60806.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072942-37552.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072942-51633.png)
A.6 | B.5 | C.5或6 | D.6或7 |
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072936-35937.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072936-79298.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072936-13788.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072936-33231.gif)
A.1 | B.![]() | C.- 2 | D.3 |
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072929-25721.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072929-68540.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072930-51399.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191013/20191013072930-45668.gif)
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