本试题主要是考查了同学们的空间想象能力和逻辑推理能力,以及计算能力的综合运用。对于面面垂直的判定定理的运用和线面垂直的判定定理和性质定理的灵活运用,是解决该试题的关键,同时也考查了二面角的求解问题,以及锥体的体积的问题的运用。
(1)要证明面面垂直,先分析线面垂直然后利用面面垂直的判定定理求证。
(2)根据二面角的大小,确定出锥体中边的问题,以及线面的位置关系,再结合锥体的体积公式求解。
证明:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232217568286301.png)
(1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221756906433.png)
平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221756984606.png)
,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221756999475.png)
平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221756984606.png)
--------------(1分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757062195.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757077406.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757109424.png)
,又
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757187235.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757374643.png)
----------------------------------(2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757389773.png)
--------------------------------------------------(3分)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757405515.png)
平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757436510.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757452839.png)
---------------------------------------------(5分)
(2)方法一:建立如图所示的空间直角坐标系,设
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757483513.png)
,那么
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757514568.png)
;
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757639608.png)
;
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757670551.png)
;
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757686573.png)
;
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757701568.png)
------(6分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757733776.png)
;
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757811780.png)
;
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758029677.png)
;
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758123669.png)
-------(7分)
假设平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758138521.png)
与平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758232523.png)
的法向量分别为
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758247708.png)
;
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758419722.png)
,那么
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758450893.png)
;
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758466975.png)
令
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758497618.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221757062195.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758840935.png)
-----------------------------------------------------------------(8分)
同理可以求得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221758965962.png)
--------------------------------------(9分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759121976.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759137838.png)
,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759215609.png)
-------------------------------(11分)
此时,正四棱柱
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759293775.png)
是棱长为1的正方体,且
四棱锥
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759417658.png)
的体积
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221756687673.png)
------------------------------(12分)
方法二:过点
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759464333.png)
作
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759480622.png)
于
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759511303.png)
,连接
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759527428.png)
,
容易证得
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759542628.png)
,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759573169.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759589413.png)
=
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759527428.png)
--------------------------------------(7分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232217596206477.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759636752.png)
,且在
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759651560.png)
中,由余弦定理可得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232217596671475.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759589413.png)
=
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759527428.png)
=
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759729459.png)
,又可证得:------------(9分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759745588.png)
,所以在
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759761691.png)
,由等面积法:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759776613.png)
=
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759807632.png)
,
即
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759870985.png)
------------(9分)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759885376.png)
,---------------------------------------------(11分)
此时,正四棱柱
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759293775.png)
是棱长为1的正方体,且
四棱锥
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221759417658.png)
的体积
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823221756687673.png)
-------------------------------------------(12分)