题目
题型:不详难度:来源:
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224751-81841.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224751-80328.png)
(1)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224751-81841.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224752-17682.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224752-89569.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224752-90196.png)
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224753-28193.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224752-90196.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224753-42619.png)
解析
试题分析:(1)数列{an}是等差数列,且a1=2,设公差为d,代入a1+a2+a3=12,求出d,求出数列{an}的通项公式;
(2)数列{an}的通项公式为an=n+2n,可以利用数列的分组求和法,分别求一个等差数列与一个等比数列的前n项和.
试题解析:(1)由已知
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224753-99075.png)
(2)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224753-58775.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224753-38048.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224753-42619.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224653-32983.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224653-49608.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224653-37498.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224654-70464.png)
A.5 | B.16 | C.80 | D.160 |
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224637-98642.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224637-79361.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224637-39727.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224638-59126.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224638-21891.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224638-46872.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224638-10037.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224639-36010.png)
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224639-57614.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224638-59126.png)
(2)设
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224639-94906.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224639-75686.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224637-39727.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224639-67041.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224640-88003.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224640-86579.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224626-82539.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224627-81025.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224627-77812.png)
A.8 | B.12 | C.16 | D.24 |
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224600-76014.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224600-53466.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224601-99498.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224601-96018.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224601-71753.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224603-78410.png)
(1)求数列
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224600-76014.png)
(2)若
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224603-94425.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224603-48658.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224604-74493.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224604-59858.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224604-59858.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224604-74493.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224532-57605.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224532-76979.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191011/20191011224532-70438.png)
A.24 | B.48 | C.96 | D.无法确定 |
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