题目内容
(本小题满分12分)
如图,三棱柱ABC—A1B1C1中,AA1
面ABC,BC
AC,BC=AC=2,D为AC的中点。
(1)求证:AB1//面BDC1;
(2)若AA1=3,求二面角C1—BD—C的余弦值;
(3)若在线段AB1上存在点
P,使得CP
面BDC1,试求AA1的长及点P的位置。
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231505365874185.jpg)
如图,三棱柱ABC—A1B1C1中,AA1
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536509108.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536509108.gif)
(1)求证:AB1//面BDC1;
(2)若AA1=3,求二面角C1—BD—C的余弦值;
(3)若在线段AB1上存在点
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536556112.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536509108.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231505365874185.jpg)
(1)AB1//面BDC1
(2)二面角C1—BD—C的余弦值:![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536603936.gif)
(3)AA1=2,点P位置是在线段AB1上且![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536603408.gif)
(2)二面角C1—BD—C的余弦值:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536603936.gif)
(3)AA1=2,点P位置是在线段AB1上且
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536603408.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231505366199645.jpg)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536634282.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536509108.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536665284.gif)
则BC
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536509108.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536509108.gif)
如图建系,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536728990.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536743809.gif)
设平面C1DB的法向量为
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536759448.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536775462.gif)
又平面BDC的法向量为
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536790541.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536806128.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536603936.gif)
(3)设
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536837606.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536853589.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536884810.gif)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536899890.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231505369151161.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536931475.gif)
所以AA1=2,点P位置是在线段AB1上且
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823150536603408.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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