题目内容
(本题满分10分) 已知三棱锥P—ABC中,PC
底面ABC,AB=BC,D、F分别为
AC、PC的中点,DE
AP于E。
(1)求证:AP
平面BDE;
(2)若AE:EP=1:2,求截面BEF分三棱锥P—ABC所成上、下两部分的体积比。
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943223108.gif)
AC、PC的中点,DE
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943223108.gif)
(1)求证:AP
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943223108.gif)
(2)若AE:EP=1:2,求截面BEF分三棱锥P—ABC所成上、下两部分的体积比。
![]() |
1:2
解:(1)证明:
平面ABC,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943410453.gif)
…………2分
由AB=BC,D为AC的中点,得![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943582341.gif)
又
………………4分
又![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943613600.gif)
由已知![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943675656.gif)
………………………5分
(2)设点E和点A到平面PBC的距离分别为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943707426.gif)
则
………………7分
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231449438471420.gif)
故截面BEF分三棱锥P—ABC所成上、下两部分体积的比为1:2。…………10分
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943395268.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943410453.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943426335.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231449435661990.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943582341.gif)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943597661.gif)
又
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943613600.gif)
由已知
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943675656.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943691462.gif)
(2)设点E和点A到平面PBC的距离分别为
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943707426.gif)
则
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823144943753624.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408231449438471420.gif)
故截面BEF分三棱锥P—ABC所成上、下两部分体积的比为1:2。…………10分
![](http://thumb2018.1010pic.com/images/loading.gif)
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