题目内容
(本小题满分12分)
如图,在四棱锥
中,底面
是平行四边形,
,且
,
,又
底面
,
,又
为边
上异于
的点,且
.
(1)求四棱锥
的体积;
(2)求
到平面
的距离.
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408231509528184751.jpg)
如图,在四棱锥
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952397347.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952428301.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952444319.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952459268.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952475286.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952553246.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952428301.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952615318.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952631204.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952646241.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952662252.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952678329.gif)
(1)求四棱锥
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952397347.gif)
(2)求
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952709200.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952724269.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408231509528184751.jpg)
(1)![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408231509528341157.gif)
(2)A到平面PED之距为![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952849272.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408231509528341157.gif)
(2)A到平面PED之距为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952849272.gif)
解:(1)在四棱锥P-ABCD中,ABCD是平行四边形,![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952896453.gif)
又AB=1,BC=2,则![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952912616.gif)
四边形ABCD面积S=![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953114311.gif)
又
…………………(6分)
(2)![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953146131.gif)
,则
,从而![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953270407.gif)
在平行四边形ABCD中,设BE=x,
则![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953286721.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953317929.gif)
由
可知:
,故
(舍)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953146131.gif)
,故面
.
故A到面PED之距而转化为A到棱PE之距
在
中,![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953707588.gif)
故A到PE之距![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953894604.gif)
从而A到平面PED之距为
……………………………………………(12分)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952896453.gif)
又AB=1,BC=2,则
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952912616.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952927125.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953114311.gif)
又
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/201408231509531301159.gif)
(2)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953146131.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953177556.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953255493.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953270407.gif)
在平行四边形ABCD中,设BE=x,
则
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953286721.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953317929.gif)
由
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953333530.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953364435.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953380272.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953146131.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953411495.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953426534.gif)
故A到面PED之距而转化为A到棱PE之距
在
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953504425.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953707588.gif)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953879341.jpg)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150953894604.gif)
从而A到平面PED之距为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140823/20140823150952849272.gif)
![](http://thumb.zyjl.cn/images/loading.gif)
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