题目内容
(本小题满分15分)
如图5,在底面为直角梯形的四棱锥![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312674430.gif)
中,
,
.
,
,
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633128451496.gif)
(1)求证:![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312861257.gif)
;
(2)求直线
;
(3)设点E在棱PC上,
,若
,求
的值。
如图5,在底面为直角梯形的四棱锥
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312674430.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082316331268972.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312720685.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312736234.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312767267.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312783311.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312830291.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633128451496.gif)
(1)求证:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312861257.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312876218.gif)
(2)求直线
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312908459.gif)
(3)设点E在棱PC上,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312923446.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312939497.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163312970190.gif)
(1)略
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313017230.gif)
(3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313032221.gif)
解(1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633130641599.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633130791154.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633130951698.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313110864.gif)
(2)在底面ABCD内过D作直线DF//AB,交BC于F,
分别以DA、DF、DP为x、y、z轴建立如图空间坐标系,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313142266.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633131571917.gif)
由(1)知![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633131881076.gif)
A(1,0,0),B(1,
,0),P(0,0,a)
,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313251286.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313313562.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633133601161.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313516755.gif)
本题也可以用几何法:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633135325340.gif)
(3)在(2)中的空间坐标系中A(1,0,0),B(1,
,0),P(0,0,a)
C(-3,
,
0),![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313922286.gif)
,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313968699.gif)
=![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314000513.gif)
,
,设
为面PAB的法向量,由
,由
,
,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314312287.gif)
由DE//面PAB得:![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633143431350.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633130641599.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633130791154.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633130951698.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313110864.gif)
(2)在底面ABCD内过D作直线DF//AB,交BC于F,
分别以DA、DF、DP为x、y、z轴建立如图空间坐标系,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313142266.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633131571917.gif)
由(1)知
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633131881076.gif)
A(1,0,0),B(1,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313204237.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313235965.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313251286.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313313562.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633133601161.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313516755.gif)
本题也可以用几何法:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633135325340.gif)
(3)在(2)中的空间坐标系中A(1,0,0),B(1,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313204237.gif)
C(-3,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313204237.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082316331376685.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313922286.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313953609.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163313968699.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633139841129.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314000513.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314156372.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314171353.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314187313.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314249573.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314280765.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314296502.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823163314312287.gif)
由DE//面PAB得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231633143431350.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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