题目内容
(本小题满分14分)如图,四棱锥P-ABCD是底面边长为1的正方形,PD⊥BC,PD=1,PC=
.
(Ⅰ)求证:PD⊥面ABCD;
(Ⅱ)求二面角A-PB-D的大小.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231513478326284.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151347817224.gif)
(Ⅰ)求证:PD⊥面ABCD;
(Ⅱ)求二面角A-PB-D的大小.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231513478326284.jpg)
(Ⅰ)略
(Ⅱ)二面角A-PB-D的大小为60°。
(Ⅱ)二面角A-PB-D的大小为60°。
(Ⅰ)证明:
,
.……2分
又
,……4分
∴ PD⊥面ABCD………6分
(Ⅱ)解:连结BD,设BD交AC于点O,
过O作OE⊥PB于点E,连结AE,
∵PD⊥面ABCD, ∴
,
又∵AO⊥BD,∴AO⊥面PDB.
∴AO⊥PB,
∵
,
∴
,从而
,
故
就是二面角A-PB-D的平面角.……………………10分
∵PD⊥面ABCD, ∴PD⊥BD,
∴在Rt△PDB中,
,
又∵
, ∴
,………………12分
∴
.
故二面角A-PB-D的大小为60°.…………………14分
(也可用向量解)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151347848523.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151347864839.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231513478951533.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151347895582.gif)
∴ PD⊥面ABCD………6分
(Ⅱ)解:连结BD,设BD交AC于点O,
过O作OE⊥PB于点E,连结AE,
∵PD⊥面ABCD, ∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151347910330.gif)
又∵AO⊥BD,∴AO⊥面PDB.
∴AO⊥PB,
∵
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151347926661.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151347957441.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151347973331.gif)
故
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151347988403.gif)
∵PD⊥面ABCD, ∴PD⊥BD,
∴在Rt△PDB中,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151348004678.gif)
又∵
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151348020502.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151348035394.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231513482071082.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823151348238494.gif)
故二面角A-PB-D的大小为60°.…………………14分
(也可用向量解)
![](http://thumb2018.1010pic.com/images/loading.gif)
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