题目内容
如图,在多面体ABCDFE中,已知面ABCD是边长为3的正方形,EF∥AB,EF=![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_ST/0.png)
A.
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_ST/1.png)
B.5
C.8.5
D.
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_ST/2.png)
【答案】分析:由题意求出VF-ABCD与几何体的体积半径,即可得到正确选项.
解答:
解:由已知条件可知,EF∥平面ABCD,
则F到平面ABCD的距离为2,
将几何体变形如图,使得EG=AB,三棱锥F-BCG的体积为:![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/images1.png)
=![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/1.png)
原几何体的体积为:
-
=![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/4.png)
故选D.
点评:本题是基础题,考查棱锥的体积,逻辑推理能力,转化思想,是常考题目.本题可以直接求解,但是麻烦.
解答:
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/images0.png)
则F到平面ABCD的距离为2,
将几何体变形如图,使得EG=AB,三棱锥F-BCG的体积为:
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/images1.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/0.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/1.png)
原几何体的体积为:
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/2.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/3.png)
![](http://thumb.zyjl.cn/pic6/res/gzsx/web/STSource/20131023212520081567693/SYS201310232125200815676003_DA/4.png)
故选D.
点评:本题是基础题,考查棱锥的体积,逻辑推理能力,转化思想,是常考题目.本题可以直接求解,但是麻烦.
![](http://thumb.zyjl.cn/images/loading.gif)
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