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(Ⅰ)证明:见解析;(Ⅱ)
![](https://img.yulucn.com/upload/4/c9/4c963daee2dcd6cb9852390ff61fe737_thumb.jpg)
,即求.
试题分析:(Ⅰ)证明AF⊥平面PCD,利用线面垂直的判定定理,只需证明AF⊥PD,CD⊥AF即可;
(Ⅱ)证明∠PBF为直线PB与平面ABF所成的角,求出PF,BF的长,即可得出结论.
(Ⅰ)证明:如图,由
![](https://img.yulucn.com/upload/a/ed/aeda0b5f32e3711b75687056bbb1a9d9_thumb.jpg)
是正三角形,
![](https://img.yulucn.com/upload/1/f4/1f469f111cb48bc5baeff5cb872b3a8e_thumb.jpg)
为
![](https://img.yulucn.com/upload/9/6a/96ab0538e07267aefc483ab9863f5f5a_thumb.jpg)
中点,所以
![](https://img.yulucn.com/upload/e/54/e54e9880f17c9139b451da04435fa209_thumb.jpg)
,又因为平面
![](https://img.yulucn.com/upload/c/77/c7731f1f57d3100cc08922fa95f0364c_thumb.jpg)
平面
![](https://img.yulucn.com/upload/4/82/482d59094b48e28af5567867037738d9_thumb.jpg)
,
且
![](https://img.yulucn.com/upload/a/2e/a2ecd18b9b1c5a9e8a2770c493fcb88f_thumb.jpg)
面
![](https://img.yulucn.com/upload/3/ae/3aef6e73e2ecf4c340e4174e11eb7fea_thumb.jpg)
面
![](https://img.yulucn.com/upload/4/82/482d59094b48e28af5567867037738d9_thumb.jpg)
;
又底面
![](https://img.yulucn.com/upload/4/82/482d59094b48e28af5567867037738d9_thumb.jpg)
为正方形,即
所以
![](https://img.yulucn.com/upload/5/87/587578f70a8bf58ab5c2c59feb5e8ddb_thumb.jpg)
平面
![](https://img.yulucn.com/upload/a/ed/aeda0b5f32e3711b75687056bbb1a9d9_thumb.jpg)
,而
![](https://img.yulucn.com/upload/b/f1/bf1fdf1dabf9fc8da4d97bd6102fc286_thumb.jpg)
平面
![](https://img.yulucn.com/upload/a/ed/aeda0b5f32e3711b75687056bbb1a9d9_thumb.jpg)
,
所以
![](https://img.yulucn.com/upload/a/ea/aea422c09bc07faa5935374a48a8a524_thumb.jpg)
,且
![](https://img.yulucn.com/upload/9/40/9407fec93fc7d5683088e52485467fa1_thumb.jpg)
,
所以
![](https://img.yulucn.com/upload/5/84/5841fc3f3f0887da12ed4a1fc7a152f3_thumb.jpg)
平面
![](https://img.yulucn.com/upload/2/80/280b79484ceda57f62e73cc16adebfe5_thumb.jpg)
.………………6分;
(Ⅱ)由(Ⅰ)证明可知,
![](https://img.yulucn.com/upload/5/87/587578f70a8bf58ab5c2c59feb5e8ddb_thumb.jpg)
平面
![](https://img.yulucn.com/upload/a/ed/aeda0b5f32e3711b75687056bbb1a9d9_thumb.jpg)
,
所以
![](https://img.yulucn.com/upload/f/f3/ff34dc2adc19e280ebc8391457d05b51_thumb.jpg)
平面
所以
![](https://img.yulucn.com/upload/5/c4/5c4665409d32401f98f6458fbeffc058_thumb.jpg)
,又由(Ⅰ)知
![](https://img.yulucn.com/upload/e/54/e54e9880f17c9139b451da04435fa209_thumb.jpg)
,且
![](https://img.yulucn.com/upload/7/b1/7b141f140c8126569c542c8b810220f4_thumb.jpg)
,
所以
![](https://img.yulucn.com/upload/2/9a/29a9a1c7336f1bb93e307f1faf3727bf_thumb.jpg)
平面
![](https://img.yulucn.com/upload/7/c1/7c15b069f5a4ae31841724323c56fdb1_thumb.jpg)
1 ,
即
![](https://img.yulucn.com/upload/e/8e/e8eee6ec6f16cf44f25f945be8cbf629_thumb.jpg)
为直线
![](https://img.yulucn.com/upload/7/c1/7c15b069f5a4ae31841724323c56fdb1_thumb.jpg)
0 与平面
![](https://img.yulucn.com/upload/7/c1/7c15b069f5a4ae31841724323c56fdb1_thumb.jpg)
1 所成的角…………………9分
且
![](https://img.yulucn.com/upload/5/73/5739be014b6c2c793d9e7372ffb6a3f8_thumb.jpg)
,易知
![](https://img.yulucn.com/upload/6/03/60350c8aac60f8c4f9863f86652cd21c_thumb.jpg)
,
![](https://img.yulucn.com/upload/1/6e/16e16f1e69d120355852c9d703d62a2b_thumb.jpg)
中,
![](https://img.yulucn.com/upload/7/57/7575acbc8f75fabbd517baaacb7b03ba_thumb.jpg)
,
所以
![](https://img.yulucn.com/upload/4/c9/4c963daee2dcd6cb9852390ff61fe737_thumb.jpg)
,即求.………………12分
点评:解题的关键是正确运用线面垂直的判定,作出线面角.
1年前
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