题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135232-85279.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135233-72502.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135233-90521.png)
(1)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135232-85279.png)
(2)设等比数列
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135233-10108.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135233-45829.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135234-53504.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135234-73345.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135234-46354.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135233-45829.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135234-91424.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135235-30854.png)
解析
试题分析:(1)由条件中等差数列
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135232-85279.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135235-49679.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135235-10890.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135235-22916.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135236-75817.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135233-10108.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135236-66745.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135234-53504.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135236-37866.png)
试题解析:(1)∵等差数列
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135232-85279.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135236-16098.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135235-49679.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135235-22916.png)
(2)由(1)可知
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135236-75817.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135233-10108.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135236-66745.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135236-37866.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135234-53504.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135058-19577.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135058-95994.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135059-98550.png)
(1)求{an}的通项公式;(2)设bn=
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135015-38890.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135007-33868.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135008-14757.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008135008-61021.png)
A.15 | B.16 | C.49 | D.64 |
A.48 | B.54 | C.60 | D.66 |
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008134737-17294.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191008/20191008134737-48418.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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