题目内容
(本题满分14分).如图,在棱长为4的正方体ABCD-A1B1C1D1中,E是D1C1上的一点且EC1=3D1 E,
(1) 求直线BE与平面ABCD所成角的正切值;
(2)求异面直线BE与CD所成角的余弦值.![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231555258806234.jpg)
(1) 求直线BE与平面ABCD所成角的正切值;
(2)求异面直线BE与CD所成角的余弦值.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231555258806234.jpg)
(1)
为直线BE与平面ABCD所成角的正切值为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155525943222.gif)
(2)异而直线BE与CD所成角的余弦值为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155525990327.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155525896395.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155525943222.gif)
(2)异而直线BE与CD所成角的余弦值为
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155525990327.gif)
(1) 在DC上取一点F, 使DF="1," 连结EF,
则EF
平面ABCD, 3分
再连结FB,则
为直线BE与平面ABCD所成角,
4分
,
故
为直线BE与平面
ABCD所成角的正切值为
……7分
(2)由题意AB//CD,
(或其补角)是异面直线![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155526426206.gif)
与DC所成的角. …9分
连结AD1与AE,在Rt△AD1E中,可得
,10分
又在Rt△BEC1中,可得
, 11分
……13分
∴异而直线BE与CD所成角的余弦值为
……14分
则EF
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155526083108.gif)
再连结FB,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155525896395.gif)
4分
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155526208270.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155526224621.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155525896395.gif)
ABCD所成角的正切值为
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155525943222.gif)
(2)由题意AB//CD,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155526411400.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155526426206.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155526458204.gif)
连结AD1与AE,在Rt△AD1E中,可得
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155526473437.gif)
又在Rt△BEC1中,可得
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155526504343.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231555265201136.gif)
∴异而直线BE与CD所成角的余弦值为
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823155525990327.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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