题目
题型:不详难度:来源:
已知
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051856-95132.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051856-53280.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051856-28480.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051857-91732.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051856-95132.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051857-54076.png)
(I)求通项
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051857-20566.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051857-91732.png)
(II)设
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051857-60463.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051857-34372.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051857-54076.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051858-22671.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051858-62659.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051858-97867.png)
(II)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051858-83118.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051859-82894.png)
解析
试题分析:(I)由题意知:
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051859-90227.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051859-80415.png)
(II)由题意知
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051859-32809.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051900-81213.png)
则
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051900-82549.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051857-54076.png)
点评:等差数列和等比数列既相互区别,又相互联系,高考作为考查学生综合能力的选拔性考试,将两类数列综合起来考查是高考的重点.学生容易出现的问题主要有两个方面:一是计算出现失误,二是不能灵活利用等差等比数列的性质,导致运算较为复杂.
核心考点
试题【 (本小题满分12分)已知是首项为,公差为的等差数列,为的前项和.(I)求通项及;(II)设是首项为1,公比为3的等比数列,求数列的通项公式及其前项和. 】;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/20191010/20191010051850-86908.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051850-79641.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051851-61877.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051850-86908.png)
已知数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051559-79770.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051600-55310.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051600-32732.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051559-79770.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051600-36007.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051600-81031.png)
(1)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051559-79770.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051601-37644.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051601-28385.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051601-19296.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051600-36007.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051601-56330.png)
若等差数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051532-81731.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051532-64857.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051532-46163.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051532-15917.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051533-17775.png)
(1)判断
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051533-99103.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051533-17775.png)
(2)若首项为
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051533-18689.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051532-81731.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051533-17775.png)
(3)若首项为
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051533-18689.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051532-81731.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051533-17775.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051534-73613.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051534-51679.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051534-44452.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051435-89291.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051435-93722.png)
已知等差数列
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051414-90441.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051414-27227.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051414-97519.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051415-60956.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051415-47684.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191010/20191010051415-99397.png)
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