解题方法
1 . 如图1,已知等边
的边长为
,点
分别是边
上的点,且满足
,如图2,将
沿
折起到
的位置.
![](https://img.xkw.com/dksih/QBM/editorImg/2023/1/15/c203c4bc-4bde-418d-a607-87274f7b3072.png?resizew=420)
(1)求证:平面
平面
;
(2)给出三个条件:①
;②平面
平面
;③四棱锥
的体积为
,从中任选一个,求平面
和平面
的夹角的余弦值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e428e7a09732be85c1224e9c8f6a71c5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5ca7d1107389675d32b56ec097464c14.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7789a500686c7a73770404ead6af0590.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7dec2ca6438c82b43f746057d8129885.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ded13d7199897d36713c8b118fb3112e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/98013a5042685a1db94249e70c62c09a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411461db15ee8086332c531e086c40c7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e8e7040c2fd8a163d71e35805775feb8.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/1/15/c203c4bc-4bde-418d-a607-87274f7b3072.png?resizew=420)
(1)求证:平面
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ca178574ce663e423e3ea16b40ee1fb6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7af6b531f532eb39c26d36e9dd97254d.png)
(2)给出三个条件:①
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/328105e90123956fed1b2e0731614a08.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/99f37a5a875bdfc4f87b63773c435575.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7af6b531f532eb39c26d36e9dd97254d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a05ceb6974c84f6728e420173edc10bc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e57f00c8225a33458a6b62bff0dcc16.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/719103f93166bab4828257608e641a9a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8a9b83d5f52042846158fa921d7e1d3e.png)
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