题目内容
(示范性高中做)
已知正方体
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134630473.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134646327.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134786235.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134802211.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134817245.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134833209.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134864352.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231441348951913.gif)
(Ⅱ)求二面角
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134911471.gif)
(Ⅲ)求三棱锥
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134942464.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134973541.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135051639.gif)
解:
(Ⅰ)连接![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135051310.gif)
连结
,则有MO∥
∥PN.所以MO∥平面NBD. ………4分
(Ⅱ)过M作MQ⊥
于Q,过Q作QR⊥BN,连结MR,
则
就是所求二面角
的平面角.
易知
∽![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135207457.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314413522373.gif)
BQ=AM=NC=
,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231441352701050.gif)
QR=
,tan
,
所以二面角
的大小为arctan
………8分
(Ⅲ)![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134973541.gif)
易知B点到底面OMN的距离=BP=![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135457272.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231441354731052.gif)
所以
=
(立方单位)………12分
(Ⅰ)连接
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135051310.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231441350671121.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135083241.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135098251.gif)
(Ⅱ)过M作MQ⊥
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135114251.gif)
则
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135129439.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134911471.gif)
易知
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135192485.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135207457.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314413522373.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231441352393332.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135254225.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231441352701050.gif)
QR=
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135285264.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135301740.gif)
所以二面角
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134911471.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135332170.gif)
(Ⅲ)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134973541.gif)
易知B点到底面OMN的距离=BP=
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135457272.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231441354731052.gif)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144134973541.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144135051639.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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