题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152347-71346.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152347-81563.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152347-71346.gif)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152347-71346.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152348-84822.gif)
解析
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152348-87730.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152348-13035.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152348-18252.gif)
当n>1时等式两边相加可得
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152348-68304.gif)
当n=1时
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152349-84405.gif)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152347-71346.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152348-84822.gif)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152257-35208.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152258-62183.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152146-86041.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152146-46033.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152147-52810.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152147-55777.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152147-61905.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152146-86041.gif)
已知数列
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152141-55829.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152142-94029.gif)
(1)若数列
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152141-55829.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152142-31927.gif)
(2)当
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152142-61399.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152141-55829.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152142-19910.gif)
已知{an}的前n项和为
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152029-69444.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011152029-79162.gif)
A.13 | B.![]() | C.46 | D.76 |
(本小题满分14分)等差数列
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151935-42028.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151935-59648.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151935-42028.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151935-66720.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151935-65856.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151936-56573.gif)
(1)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151935-42028.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151936-75045.gif)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151936-13189.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151936-49876.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151937-34000.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151937-37461.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011151937-61644.gif)
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