1 . 在中国古代数学著作《就长算术》中,鳖臑(biēnào)是指四个面都是直角三角形的四面体.如图,在直角
中,
为斜边
上的高,
,
,现将
沿
翻折
,使得四面体
为一个鳖臑,则直线
与平面
所成角的余弦值是______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0faed94a64b2dcfc6801b4fca0f16675.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/efc6e4b936d7a800e839a30c3839574d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a8a7b5adfcac0f46a4cd19da4ebb4a2b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/db5e1441a49e782ff0ef46e776cde06a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/88c46b92d7ff7055a3428852e745b263.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d35dbf75101e6d032b64720fccfeaa46.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ab41cce6eb2d3058a644314865d16548.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8d78fc7fcb2762de28dcef8aa3aa0e49.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/10/27/a28cc90a-4f84-47c7-9537-11af40e2c73b.png?resizew=376)
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3卷引用:2020年1月浙江省杭州市余杭区部分学校学考高三数学试题
名校
2 . 计算:![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a5dcb135fca39a744d85609436852afd.png)
______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a5dcb135fca39a744d85609436852afd.png)
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9卷引用:2015年四川省普通高中学业水平测试试题