题目内容
如图5,
是半径为a的半圆,AC为直径,点E为
的中点,点B和点C为线段AD的三等分点.平面AEC外一点F满足
,FE=
a .
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314330519685.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231433052115425.jpg)
图5
(1)证明:EB⊥FD;
(2)已知点Q,R分别为线段FE,FB上的点,使得
,求平面
与平面
所成二面角的正弦值
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305133407.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305133357.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305164431.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305180237.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314330519685.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231433052115425.jpg)
图5
(1)证明:EB⊥FD;
(2)已知点Q,R分别为线段FE,FB上的点,使得
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305227752.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305258274.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305274302.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305289362.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231433053053470.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314330533634438.jpg)
(2)设平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305258274.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305367249.gif)
由BQ=
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305383228.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305383228.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305398351.gif)
而
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305414260.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305430279.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305445278.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305430279.gif)
而平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305430279.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305508152.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305274302.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305367249.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305539459.gif)
由(1)知,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305554241.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305570108.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305430279.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305367249.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305570108.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305430279.gif)
而
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305648268.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305430279.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314330567985.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305866266.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305430279.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143306038523.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143306054298.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305258274.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305274302.gif)
在
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143306100458.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143306132940.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143306132945.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143306272945.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314330628823620.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231433063031167.gif)
故平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305258274.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314330633472.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305274302.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143305289362.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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