题目内容
(本小题满分12分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231439268044434.jpg)
如图,在四棱锥
中,
⊥平面
,
⊥平面
,
,
.
(1) 证明:
;
(2) 点
为线段
上一点,求直线
与平面
所成角的取值范围.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231439268044434.jpg)
如图,在四棱锥
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926804448.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926835235.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926866279.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926882242.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926866279.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926913640.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926928503.gif)
(1) 证明:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926944534.gif)
(2) 点
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926960202.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926835235.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926991237.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927006278.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231439270222397.jpg)
18.解法1:取
的中点
,连
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231439270841572.gif)
∵
,∴
. 又
⊥平面
.
以
为原点建立空间直角坐标系
,如图,
则已知条件有:
,
……………………………………2分
.
设平面
的法向量为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927350475.gif)
则由![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927381888.gif)
及![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231439273961079.gif)
解得
.可取
…………………4分
又
⊥平面
. ∴
.又
,∴
⊥平面
.
∴平面
的法向量可取为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927599499.gif)
∵
∴
⊥
,∴
. ………6分
(2)平面
的一个法向量记为
,
则
,即![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231439277712059.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314392778630573.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927038241.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927053209.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927069241.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231439270841572.gif)
∵
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927100323.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927116333.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926835235.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926866279.gif)
以
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927053209.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927162392.gif)
则已知条件有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927178910.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927303701.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927318810.gif)
设平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927334275.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927350475.gif)
则由
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927381888.gif)
及
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231439273961079.gif)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927412352.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927428368.gif)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926835235.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926866279.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927521325.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927116333.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927069241.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927568270.gif)
∴平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927568270.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927599499.gif)
∵
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927615721.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927646199.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927662207.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143926944534.gif)
(2)平面
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927006278.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927740467.gif)
则
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823143927755683.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231439277712059.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/2014082314392778630573.jpg)
![](http://thumb2018.1010pic.com/images/loading.gif)
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