已知
的夹角为
,则![](https://img.xkw.com/dksih/QBM/2016/1/27/1572468370423808/1572468376084480/STEM/135a83cb87ea452dbe00f0041a52886c.png?resizew=61)
_______ .
![](https://img.xkw.com/dksih/QBM/2016/1/27/1572468370423808/1572468376084480/STEM/a9be3b588b544625aff8f782f80a4bb4.png?resizew=113)
![](https://img.xkw.com/dksih/QBM/2016/1/27/1572468370423808/1572468376084480/STEM/cd49cd25e2e64fa393405d7e921c6062.png?resizew=27)
![](https://img.xkw.com/dksih/QBM/2016/1/27/1572468370423808/1572468376084480/STEM/135a83cb87ea452dbe00f0041a52886c.png?resizew=61)
更新时间:2016-12-04 01:38:00
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【知识点】 向量在几何中的应用