已知正四面体
中,
,
分别是线段
,
的中点,点
是线段
上靠近
的四等分点,则直线
与
所成角的余弦值为________ .
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
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更新时间:2021-12-25 17:55:08
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