1 . 如图,在四棱锥
中,
平面
,底面
是菱形,
,
,
,
分别是棱
的中点.
![](https://img.xkw.com/dksih/QBM/editorImg/2023/1/3/2c3ae9c9-ad07-48d8-b6a2-648bae048570.png?resizew=208)
(1)证明:
平面
;
(2)求二面角
的余弦值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0585b6c0f156eecf9662b9846d4eb693.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ccd4fd4b7a4d6b8ca0c5827c055a9ce7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bb8fb552b9e21dbaba74d11aa747790.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fcd0ced286a0fbc7e4862f8147264277.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6184f3b929dda3c1b3b35b9aec448118.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ad056c25c0fdcbcc765eb5cbc6093f2b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/47891397990336f55f96bd66d367758b.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/1/3/2c3ae9c9-ad07-48d8-b6a2-648bae048570.png?resizew=208)
(1)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/06222ee533c2484ab25321a6abbf98cb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/852aabd89edffc1b94344ff3f1f31ccd.png)
(2)求二面角
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/053af8641980763a7f0e77beefe0712d.png)
您最近一年使用:0次
2 . 如图,⊙O的半径OB垂直于直径AC,D为AO上一点,BD的延长线交⊙O于点E,过E点的圆的切线交CA的延长线于点P.
求证:PD2=PA•PC
求证:PD2=PA•PC
![](https://img.xkw.com/dksih/QBM/2018/11/16/2076809708109824/2078307597312000/STEM/23a2012e-b378-468a-81a7-84d80fbd22c3.png?resizew=186)
您最近一年使用:0次