题目内容
(本小题8分)
如图,正方形ABCD和四边形ACEF所在的平面互相垂直. EF//AC,AB=
,CE=EF=1,
.
(1)求证:AF//平面BDE;
(2)求异面直线AB与DE所成角的余弦值.![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231611563575302.jpg)
如图,正方形ABCD和四边形ACEF所在的平面互相垂直. EF//AC,AB=
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156326224.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156342491.gif)
(1)求证:AF//平面BDE;
(2)求异面直线AB与DE所成角的余弦值.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231611563575302.jpg)
(1)略
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156373223.gif)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156373223.gif)
(1)证明:
是正方形,且AB=
,
AO=1,又
//
,EF=1,
EFAO为平行四边形,则
//
,而
,
,
AF//面BDE ………………………………………………(3分)
(2)解:
是正方形,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
//![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156638242.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
为异面直线AB与DE所成的角或其补角 …………………………(2分)
又
,又面ABCD
面ACEF,且面ABCD
面ACEF=AC
BD
面ACEF,又
,
BD
OE.
而由EC=1,OC=OA=1,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156825483.gif)
OE=1,又OD=1,则ED=![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156856493.gif)
又CD=
,CE="1," ![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156903909.gif)
异面直线AB与DE所成的角的余弦值为
……………………………………(3分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156388325.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156404225.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156451232.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156466238.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156498232.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156513239.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156529538.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156544418.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
(2)解:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156388325.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156622235.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156638242.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156669403.gif)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156685329.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156700108.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156716134.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156700108.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156778556.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156700108.gif)
而由EC=1,OC=OA=1,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156825483.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156856493.gif)
又CD=
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156404225.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156903909.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156435128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823161156373223.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目