题目
题型:不详难度:来源:
数列{
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004619-89492.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004620-30423.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004620-81977.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004620-65794.png)
(1)求数列的通项公式;
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004620-81042.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004621-68307.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004621-29409.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004621-25398.png)
解析
试题分析:解:(1)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004620-65794.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004621-71755.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004622-75685.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004622-84744.png)
设
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004622-85119.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004623-49290.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004623-97158.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004621-29409.png)
(2)∵
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004621-29409.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004623-92779.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004623-34053.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004623-92726.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004624-29671.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004623-34053.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004623-92779.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004624-61447.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004624-29371.png)
∴当
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004623-92726.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004620-81042.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004624-25254.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004624-31662.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004625-42502.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004625-13716.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004620-81042.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004625-24130.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004625-72893.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004621-25398.png)
点评:解决数列的求和要注意通项公式的特点,然后回归常规的公式来求解运算,属于基础题。
核心考点
举一反三
在单调递增数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004538-61792.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004538-21553.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004539-84565.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004539-69694.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004539-64527.png)
(Ⅰ)求
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004539-72544.png)
(Ⅱ)判断数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004538-61792.png)
(Ⅲ)设
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004540-84849.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004540-86718.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004539-64527.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004540-43789.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004352-50465.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004353-59831.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004353-33049.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004353-94830.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004353-12179.png)
A.15 | B.18 | C.9 | D.12 |
等差数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004343-88830.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004343-28556.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004343-70029.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004344-59256.png)
(Ⅰ)求
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004343-88830.png)
(Ⅱ)设
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004344-29521.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004344-77020.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004343-28556.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004345-13535.png)
已知数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004220-78399.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004220-63327.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004220-23181.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004220-99543.png)
(Ⅰ)求
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004221-13817.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004221-77654.png)
(Ⅱ)若
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004221-86229.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004221-34489.png)
(Ⅲ)若
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004221-16571.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004222-40447.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004222-54523.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004212-82951.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004212-74675.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010004213-66487.png)
A.58 | B.88 | C.143 | D.176 |
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