1 . 如图,直三棱柱
中,
分别为
的中点.
![](https://img.xkw.com/dksih/QBM/2019/7/11/2244716688785408/2245255655915520/STEM/8bb00a01-ec53-4bbd-bba0-59c44e53e0d8.png)
(1)证明:
平面
;
(2)求
与平面
所成角的正弦值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/42d3a82b8e587ee890467835bc4e854c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/01afbdff592e2e269e1dbf751ab1ef5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bbfb9c088a7422e95f747701a626513d.png)
![](https://img.xkw.com/dksih/QBM/2019/7/11/2244716688785408/2245255655915520/STEM/8bb00a01-ec53-4bbd-bba0-59c44e53e0d8.png)
(1)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/92bced6bf70db7229db85f2b10339431.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c09afc70f448545336304333d5b5658b.png)
(2)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d88bf46ad08f9677c37eed1d0369329.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c09afc70f448545336304333d5b5658b.png)
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2019-07-12更新
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4卷引用:西藏日喀则市2020届高三上学期学业水评测试(模拟)数学(理)试题