题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083425-99048.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083425-32719.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083425-99048.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083426-16855.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083425-32719.png)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083426-37695.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083426-70841.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083426-67624.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083426-90612.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083427-68015.png)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083427-13685.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083427-66463.png)
解析
(Ⅰ)先根据等差数列的通项公式和求和公式求得an和Sn.
(Ⅱ)根据等比数列的通项公式求得{bn-an}的通项公式,根据(1)中的an求得bn,可知数列{bn}是由等差数列和等比数列构成,进而根据等差数列和等比数列的求和公式求得Tn
解:(1)因为
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083425-99048.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083427-57654.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083426-90612.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083428-83338.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083427-68015.png)
(2)因为
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083426-37695.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083428-52022.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083428-81116.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083427-13685.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083428-75883.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083428-37236.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083429-30192.png)
核心考点
试题【(本小题满分14分)已知是首项为19,公差d=-2的等差数列,为的前n项和.(1)求通项公式及;(2)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n】;主要考察你对等比数列等知识点的理解。[详细]
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083419-83491.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083419-98287.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083419-98287.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083419-41735.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083419-45546.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083419-23762.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083419-98287.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083419-98287.png)
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083414-68407.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083414-39916.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083414-86508.png)
A.![]() | B.![]() | C.![]() | D.![]() |
A.-4 | B.-1 | C.1或4 | D.-1或-4 |
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083401-92250.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083402-25257.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083403-37357.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083356-58441.png)
(I)证明数列
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083356-86693.png)
(II)设
![](http://img.shitiku.com.cn/uploads/allimg/20191014/20191014083357-21719.png)
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