题目内容
数列
的前n项和为
,若数列
的各项按如下规律排列:![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232120427631455.png)
(1)
__________
(2)给出如下三个命题
①.数列
是等比数列;
②.数列
的前n项和为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823212042809700.png)
③.若存在正整数
,使![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232120428411062.png)
其中正确的序号有 .(将你认为正确的结论序号都填上)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823212042700451.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823212042731388.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823212042700451.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232120427631455.png)
(1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823212042778403.png)
(2)给出如下三个命题
①.数列
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232120427781039.png)
②.数列
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232120427781039.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823212042809700.png)
③.若存在正整数
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823212042825312.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232120428411062.png)
其中正确的序号有 .(将你认为正确的结论序号都填上)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823212042856410.png)
解:根据数列的规律,分母为n时,所对应的项数是(n-1)项.从分母是2开始到分母为n结束共有[n(n-1)]/2项
前24项构成的数列是:1/2,1/3,2/3,1/4,2/4,3/4,1/5,2/5,3/5,4/5,1/6…1/8,2/8,3/8
②数列a1,a2+a3,a4+a5+a6,a7+a8+a9+a10,…实际上是1/2,1,6/4,2,…n-1/2,再由数列定义判断
②数列a1,a2+a3,a4+a5+a6,a7+a8+a9+a10,…实际上是1/2,,1,6/4,2,…n-1/2,先判断数列类型,再用求其前n项和.
③通过②的前n项和解不等式,确定k的值,从而再判断终止的项.
前24项构成的数列是:1/2,1/3,2/3,1/4,2/4,3/4,1/5,2/5,3/5,4/5,1/6…1/8,2/8,3/8
②数列a1,a2+a3,a4+a5+a6,a7+a8+a9+a10,…实际上是1/2,1,6/4,2,…n-1/2,再由数列定义判断
②数列a1,a2+a3,a4+a5+a6,a7+a8+a9+a10,…实际上是1/2,,1,6/4,2,…n-1/2,先判断数列类型,再用求其前n项和.
③通过②的前n项和解不等式,确定k的值,从而再判断终止的项.
![](http://thumb2018.1010pic.com/images/loading.gif)
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