题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021723-50453.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-60443.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-11776.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-49400.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-57755.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-95440.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-44170.png)
(1)分别求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021723-50453.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-49400.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-44161.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-50230.png)
(2)设数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-81522.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-39704.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-18484.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-12551.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-92418.png)
解析
试题分析:(1)首先设出公差和公比,根据已知条件及等比数列和等差数列的性质,列方程组解方程组,求得公差和公比,写出各自的通项公式;(2)因为
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-49400.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
试题解析:(1)设数列
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-59832.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021726-89718.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-49400.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021726-49934.png)
由已知得
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021726-34226.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021726-75079.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-39704.png)
又
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021726-11917.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021727-43676.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021727-30847.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-18484.png)
(2)当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021727-72837.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021727-92173.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021728-15524.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021728-97698.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021728-29485.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021728-83579.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021728-10723.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021729-69938.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021729-44023.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021729-12500.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021729-19338.png)
所以当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021729-91778.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021730-62307.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021730-14779.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021730-35948.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021730-96468.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021731-55010.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021731-17471.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021731-58900.png)
所以当
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-92418.png)
比较一下这两种情况下的
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-62431.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021725-92418.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021724-59807.png)
核心考点
试题【已知数列是等差数列,且,;又若是各项为正数的等比数列,且满足,其前项和为,.(1)分别求数列,的通项公式,;(2)设数列的前项和为,求的表达式,并求的最小值.】;主要考察你对等差数列等知识点的理解。[详细]
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021654-49319.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021654-76365.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021654-82404.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021655-52498.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021655-50098.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021649-42018.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021649-87488.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021650-87694.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021649-42018.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021650-46471.png)
A.4 | B.5 | C.6 | D.7 |
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021627-50046.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021627-90156.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021627-73667.png)
A.![]() | B.12 | C.![]() | D.6 |
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021616-51503.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021616-96203.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021616-83867.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021616-68649.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021617-69590.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021617-35305.png)
A.15 | B.16 | C.17 | D.18 |
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021551-40923.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021551-77009.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191012/20191012021551-18018.png)
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