题目内容
给出下列命题:
①常数列既是等差数列,又是等比数列;
②
;
③在数列
中,如果
前项和
,则此数列是一个公差为4的等差数列;
④若向量
方向相同,且
,则
与
方向相同;
⑤
是等比数列,
为其前
项和,则
成等比数列。
则上述命题中正确的有 (填上所有正确命题的序号)。
①常数列既是等差数列,又是等比数列;
②
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231420115591069.gif)
③在数列
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011590380.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011606192.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011653449.gif)
④若向量
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011668250.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011684308.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011700253.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011731249.gif)
⑤
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011590380.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011746220.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011606192.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823142011778555.gif)
则上述命题中正确的有 (填上所有正确命题的序号)。
②④⑤
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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