题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040650-50108.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040650-81090.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040650-45212.png)
①求
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040650-50108.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040651-79926.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040650-50108.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040651-13992.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040651-65067.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040651-92321.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040651-22643.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040651-65067.png)
解析
试题分析:(1)由已知得:
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040652-98407.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040652-50259.png)
∴
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040651-92321.png)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040652-13982.png)
∴当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040651-22643.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040651-65067.png)
点评:中档题,确定等差数列的通项公式,往往利用已知条件,建立相关元素的方程组,以达到解题目的。公差不为0时,等差数列的前n项和,是关于n的二次函数,因此,可利用二次函数图象和性质确定最值。
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040633-65210.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040633-67889.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040634-56736.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040644-89970.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040644-57171.png)
①求
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040633-65210.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040645-78739.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040645-73458.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040633-67889.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040645-64797.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040606-72193.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040606-45333.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040606-48951.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040606-84283.png)
①设
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040607-40221.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040607-26467.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040607-80716.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040607-30781.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040607-86957.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040608-75553.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040559-34562.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040600-22305.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040600-78281.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040600-22972.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040600-22305.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040600-41119.png)
A.6 | B.7 | C.8 | D.9 |
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040548-82569.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040548-98670.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040548-96377.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040554-37826.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040554-12101.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040555-64425.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040555-52877.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040525-57639.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040526-42307.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040526-45254.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040525-57639.png)
(2)将{
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040525-57639.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040526-92474.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040526-94548.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040526-67326.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040527-93038.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040527-13427.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012040527-29218.png)
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