题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090521-55247.png)
(1)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090522-13107.png)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090522-32508.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090522-71526.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090522-95600.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090523-47023.png)
解析
试题分析:(1)设在等比数列
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090523-49026.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090523-82062.png)
根据因为
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090523-20272.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090523-82062.png)
(Ⅱ)由(I)可得
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090524-45362.png)
此类问题的解答,要特别注意和式中的“项数”.
试题解析:(1)设在等比数列
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090523-49026.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090523-82062.png)
因为
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090523-20272.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090524-49501.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090524-26324.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090524-16769.png)
解得
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090524-59064.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090522-95600.png)
(Ⅱ)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090524-45362.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090525-93188.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090525-16229.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090525-58509.png)
①—②,得
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090526-10906.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090526-65939.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090526-55255.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090526-26267.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090526-27202.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090523-47023.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090340-64675.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090340-21372.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090340-83613.png)
A.50 | B.45 | C.55 | D.40 |
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090258-44687.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090258-99022.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090258-76325.png)
(1)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090258-44687.png)
(2)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090258-44687.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090258-98829.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090259-54451.png)
(3)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090259-90005.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090258-98829.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090259-84289.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090216-89384.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090216-84887.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090217-15582.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090217-19673.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090109-92396.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090109-90108.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090109-29646.png)
(Ⅰ)证明数列
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090109-92396.png)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090109-68599.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090109-16553.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090110-76279.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090110-77094.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090032-87294.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090032-59249.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009090033-22564.png)
A.2 | B.3 | C.4 | D.2或3 |
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