题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112702-80942.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112702-20116.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112702-78858.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112703-91715.png)
(Ⅰ)求
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112703-63782.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112703-71228.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112703-27880.png)
(Ⅱ)记数列{an}前2n项和为
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112703-11422.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112703-11422.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-89980.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-92515.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-56941.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-19234.png)
解析
试题分析:本题考查等差数列的通项公式和前
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-89980.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-89980.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-89980.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-89980.png)
试题解析:(I)∵
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112705-64499.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112702-78858.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-92515.png)
由题意可得数列
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112711-83176.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-89980.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112711-54986.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-89980.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112711-57804.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-56941.png)
(II)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112712-79799.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112712-30970.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112712-67257.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112712-69528.png)
结合二次函数的性质可知,当
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112704-19234.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112248-32854.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112248-99847.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112248-40244.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112248-24452.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112249-50020.png)
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112240-35853.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112241-98993.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112240-35853.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112241-67090.png)
A.63 | B.109 | C.117 | D.210 |
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112204-45777.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112207-25241.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112204-45777.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009112208-64707.png)
A.63 | B.109 | C.117 | D.210 |
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111750-23132.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111750-46753.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111751-66162.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111751-50965.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111751-40440.png)
A.24 | B.32 | C.48 | D.64 |
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111701-53827.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111702-30391.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111701-53827.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111702-66068.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111702-79951.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111702-61526.png)
(Ⅰ)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111701-53827.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111702-66068.png)
(Ⅱ)是否存在常数a,使得
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111703-10712.png)
(Ⅲ)是否存在
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111703-64585.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111703-93567.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191009/20191009111703-11295.png)
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