题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090822-54725.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090823-93060.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090823-93060.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090823-35933.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090823-20029.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090823-65621.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090824-97311.png)
(Ⅰ)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090822-54725.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090823-20029.png)
(Ⅱ)设
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090824-34798.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090835-91797.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090835-18407.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090835-27176.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090835-31974.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090841-40377.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-63825.png)
解析
(Ⅰ)当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-10669.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-23869.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-93850.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-39268.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-10669.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090843-35234.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090843-22019.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090843-58716.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090843-29787.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090823-20029.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090844-23135.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090844-14235.png)
(2)由(1)可知
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090844-71362.png)
,然后利用错位相减法得到求和。
解:(1)当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-10669.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-23869.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-93850.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-39268.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090842-10669.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090843-35234.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090843-22019.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090843-58716.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090843-29787.png)
又因为
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090823-20029.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090844-23135.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090844-14235.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090844-88214.png)
(2)由(1)可知
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090844-71362.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090845-43247.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090845-20179.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090845-34555.png)
①-②得:
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090846-88227.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090846-66464.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090846-97355.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090846-42953.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090846-59524.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090806-90620.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090806-85219.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090806-42931.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090807-84572.png)
列的
A.第9项 | B.第8项 | C.第7项 | D.第6项 |
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090753-86425.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090754-80771.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090754-26907.png)
A.![]() | B.![]() | C.![]() | D.![]() |
已知数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090737-47511.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090737-44104.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090738-88087.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090738-61866.png)
(Ⅰ)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090737-47511.png)
(Ⅱ)已知数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090738-67074.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090738-47009.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090738-99779.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090739-32258.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090737-44104.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090739-64989.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090725-34753.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090725-29002.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090725-23481.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090725-77599.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090725-25695.png)
A.16 | B.8 | C.4 | D.2 |
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090717-88100.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090717-32494.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090717-44668.png)
(Ⅰ)设
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090717-53923.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090717-17039.png)
(Ⅱ)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090717-88100.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090717-67209.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012090717-30691.png)
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