真题
解题方法
1 . 在三棱锥
中,
是边长为4的正三角形,平面
平面
,
,M、N分别为
的中点.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/12/a48120a9-5269-422e-94d0-95e5489d843e.png?resizew=176)
(1)证明:
;
(2)求二面角
的大小;
(3)求点B到平面
的距离.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/41e5db1d2fd912f77923e4c120a7dc19.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/78307cd417504554a4e2276fe24d1162.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3d7bde9982692ba3a587e7f6e3b46a4d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7b7e126ea4db87e547eaccd2ee236108.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/12/a48120a9-5269-422e-94d0-95e5489d843e.png?resizew=176)
(1)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/90fa715d27ae43ec1e157226bc9dea54.png)
(2)求二面角
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6177f4876d8f05b8fe9a9618756ad22f.png)
(3)求点B到平面
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/70db40c42655327adee01caedfc9d50c.png)
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