题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-69886.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-84277.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-56437.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-84896.png)
(1)求首项
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-90444.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100911-79450.png)
(2)若
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100911-21222.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-84277.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100911-26690.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100911-92026.png)
解析
(1)由于等差数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-69886.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-84277.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-56437.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100910-84896.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100912-82954.png)
(3)在第一问中
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100912-97540.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100912-61250.png)
解:(1)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100912-87672.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100912-27299.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100913-99854.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100912-82954.png)
解得
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100911-26690.png)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100912-97540.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100913-97066.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100911-92026.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100858-69777.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100858-64667.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100858-46314.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100635-88546.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100635-41107.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100636-88766.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100635-88546.png)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100635-88546.png)
(2)若数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100636-32670.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100636-12389.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100636-32670.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100457-31099.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100458-43334.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100458-83674.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100458-66573.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100458-82849.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100459-25185.png)
(1)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100457-31099.png)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100459-85201.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100459-30225.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100459-11713.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100500-57771.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100500-43655.png)
(3)设
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100506-10062.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010100506-23280.png)
A.21 | B.20 | C.19 | D.18 |
A.a1·a8>a4·a5 | B.a1·a8<a4·a5 |
C.a1·a8=a4·a5 | D.以上答案均可能 |
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