题目内容
已知共有![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708293320.png)
项的数列
,
,定义向量
、![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708402715.png)
,若
,则满足条件的数列
的个数为 ▲ .
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708293320.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708324618.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708339464.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708355421.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708386657.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708402715.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708417779.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708449553.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708339464.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708495395.png)
∵cn向量的模=dn向量的模
∴a
n+a
(n+1)=n
+(n+1) ![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708527243.png)
∴a
(n+1)=n
+(n+1)
- a
n
∴ a(n+1)=±![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708683705.png)
a1=2, 1种选择;A2 ,2种选择;......,ak,2种选择
由乘法原理{An}共
种方法
∴a
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708527243.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708527243.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708527243.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708527243.png)
∴a
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708527243.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708527243.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708527243.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708527243.png)
∴ a(n+1)=±
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708683705.png)
a1=2, 1种选择;A2 ,2种选择;......,ak,2种选择
由乘法原理{An}共
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823205708683392.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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