已知
,
均为单位向量,它们的夹角为
,那么![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b7df5d272bcef79e8858224694d433bf.png)
__________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/969604545902c9a66549a4a44ec3a3c6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/90ab17fd4247cdd710c363d5d3fbc5bd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b7df5d272bcef79e8858224694d433bf.png)
更新时间:2018-07-02 11:06:10
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