题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035445-10561.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035445-87003.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035446-33397.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035446-12806.png)
A.有3个 | B.有2个 | C.有1个 | D.不存在 |
答案
解析
试题分析:
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035446-59490.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035446-14780.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035447-55205.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035447-96962.png)
此时从
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035447-41182.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035447-60256.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035447-85089.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035448-54962.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035448-57574.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035448-87458.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035448-43642.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035449-28573.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035449-22414.png)
点评:本题中数列求和要依据通项公式特点分两种情况,分别讨论所求各项所属的范围及应代入的公式,第二种情况找到各项中正负项分界的位置是难点
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035421-23145.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035421-46435.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035421-69451.png)
(Ⅰ)设
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035422-11959.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035422-48583.png)
(Ⅱ)证明:
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035422-69871.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035410-99724.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035410-68396.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035410-30658.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035411-76258.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035411-62987.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035411-58475.png)
(Ⅰ)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035410-99724.png)
(Ⅱ)若
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035411-45611.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035412-65000.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035412-87498.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035412-84454.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035402-71735.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035402-72093.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035402-66905.png)
(1)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035403-95328.png)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035403-70617.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035346-37730.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035346-23911.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035346-60153.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035346-42589.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035346-55102.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035347-37806.png)
(Ⅰ)求
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035347-13845.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035347-27616.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035346-23911.png)
(Ⅱ)求数列{
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035347-42244.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035347-52916.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035338-97612.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035339-88871.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035339-18685.png)
(1)求数列的通项公式; (2)求
![](http://img.shitiku.com.cn/uploads/allimg/20191015/20191015035339-28485.png)
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