题目内容
(本小题满分13分)
如图,平行四边形
中,
,
,且
,正方形
所在平面与平面
垂直,
分别是
的中点.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231631058612258.gif)
(1)求证:
;
(2)求证:
平面
;
(3)求三棱锥
的体积.
如图,平行四边形
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105643303.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105658279.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105689386.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105705340.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105721412.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105643303.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105767261.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105783323.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231631058612258.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082316310587772.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105892455.gif)
(2)求证:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105939273.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105955275.gif)
(3)求三棱锥
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105970419.gif)
(1)略
(2)略
(3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105986968.gif)
(Ⅰ)证明:平面![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105721412.gif)
平面
,交线为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106189237.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106204183.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106220331.gif)
∴
----------2分
∴![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106267331.gif)
又![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106204183.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105705340.gif)
∴
--------4分
(Ⅱ)证明:连结
,则
是
的中点
∴
中,
---------------6分
又![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106204183.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106547332.gif)
∴![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105939273.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106579242.gif)
∴
平面
-------------8分
(Ⅲ)解:设
中
边上的高为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106688200.gif)
依题意:![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106703591.gif)
∴![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106719434.gif)
即:点
到平面
的距离为
---------------10分
∴
-----------------13分
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105721412.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106157108.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105643303.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106189237.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106204183.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106220331.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106235606.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106267331.gif)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106204183.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105705340.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105892455.gif)
(Ⅱ)证明:连结
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106329228.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106345213.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106360234.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106454404.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106469345.gif)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106204183.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106547332.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105939273.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106579242.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105939273.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163105955275.gif)
(Ⅲ)解:设
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106657454.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106672241.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106688200.gif)
依题意:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106703591.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106719434.gif)
即:点
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106735205.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106750270.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106766269.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163106781968.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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