名校
1 . 已知四棱锥
的底面ABCD是平行四边形,侧棱
平面ABCD,点M在棱DP上,且
,点N是在棱PC上的动点(不为端点).
![](https://img.xkw.com/dksih/QBM/editorImg/2022/9/30/3ca3f34b-c460-4557-a4c9-0502b91ee703.png?resizew=220)
(1)若N是棱PC中点,完成:
(i)画出
的重心G(在图中作出虚线),并指出点G与线段AN的关系:
(ii)求证:![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d2be49c37e30a3ced0364c3e74d8c687.png)
平面AMN;
(2)若四边形ABCD是正方形,且
,当点N在何处时,直线PA与平面AMN所成角的正弦值取最大值.
![](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/fc85ce5e111acf7162b8e1b5a3f6b220.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/9/30/3ca3f34b-c460-4557-a4c9-0502b91ee703.png?resizew=220)
(1)若N是棱PC中点,完成:
(i)画出
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/acee03d4bb4667b6c345221b6c9b0fa4.png)
(ii)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d2be49c37e30a3ced0364c3e74d8c687.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/638537c0a30676c73fea76c80e0f8bd0.png)
(2)若四边形ABCD是正方形,且
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f2304c541406034dd83040e9a7887ed7.png)
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