题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085618-37873.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085618-88145.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-90848.png)
(Ⅰ)写出
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085618-88145.png)
(Ⅱ)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-83186.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-82946.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-36070.png)
解析
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-90848.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085620-57022.png)
从而得到
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085620-73962.png)
(II)先由Sn,可得an,再根据an可确定从第几项开始an<0,然后分段讨论求
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-83186.png)
(Ⅰ)由题设得
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085620-57022.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085620-73962.png)
(Ⅱ)当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085620-83493.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085620-97241.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085621-71262.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085621-25968.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085621-17467.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085621-36458.png)
由于此时-2×1+13=11=
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085621-99745.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085618-37873.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085622-46775.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085622-63133.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085618-37873.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-83186.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085622-65303.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085622-72561.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085623-71377.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085623-24769.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-82946.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085623-36175.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085624-21096.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085624-92378.png)
=
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085624-40177.png)
=
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085624-31970.png)
=
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085625-46649.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085625-78694.png)
所以数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-83186.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085619-36070.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085603-73954.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085603-93004.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085603-30216.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085604-81759.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085604-99143.png)
(Ⅰ)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085603-73954.png)
(Ⅱ)记
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085604-93261.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085604-23335.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085603-30216.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085605-49143.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085556-47305.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085556-66038.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085556-89406.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085556-52222.png)
(Ⅰ)求证:数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085556-69708.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085557-36665.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085556-66038.png)
(Ⅱ)若数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085557-38615.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085556-66038.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085557-86665.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085557-68731.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085556-66038.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085546-35531.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085546-54347.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085547-51748.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085547-72715.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085547-76593.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085540-46166.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085541-87924.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085541-89600.png)
A.![]() | B.![]() | C.![]() | D.![]() ![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085515-74359.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085516-83342.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085516-81486.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085516-69276.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085516-63936.png)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085515-74359.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085516-81486.png)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085517-55120.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085517-75389.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085517-49591.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085516-63936.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012085517-75389.png)
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