满分5 >
高中数学试题 >
正三棱锥V-ABC(顶点在底面的射影是底面正三角形的中心)中,D,E,F分别是V...
正三棱锥V-ABC(顶点在底面的射影是底面正三角形的中心)中,D,E,F分别是VC,VA,AC的中点,P为VB上任意一点,则直线DE与PF所成的角的大小是( )
A.30°
B.90°
C.60°
D.随P点的变化而变化
考点分析:
相关试题推荐
已知在三棱锥A-BCD中,M,N分别为AB,CD的中点 则下列结论正确的是( )
A.MN≥
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072010_ST/0.png)
(AC+BD)
B.MN
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072010_ST/1.png)
C.MN=
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072010_ST/2.png)
(AC+BD)
D.MN<
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072010_ST/3.png)
(AC+BD)
查看答案
在三棱锥A-BCD中,AC⊥底面BCD,BD⊥DC,BD=DC,AC=a,∠ABC=30°,则点C到平面ABD的距离是( )
A.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072009_ST/0.png)
B.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072009_ST/1.png)
C.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072009_ST/2.png)
D.
查看答案
在正方体ABCD-A
1B
1C
1D
1中,直线AC
1与平面ABCD所成的角为θ,则sinθ值为( )
A.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072008_ST/0.png)
B.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072008_ST/1.png)
C.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072008_ST/2.png)
D.
查看答案
在△ABC中,角A,B,C所对的边长分别为a,b,c,若∠C=120°,c=
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072007_ST/0.png)
a,则( )
A.a>b
B.a<b
C.a=b
D.a与b的大小关系不能确定
查看答案
在△ABC中,角A、B、C的对边分别为a、b、c,且a=λ,b=
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103100029637607293/SYS201311031000296376072006_ST/0.png)
λ(λ>0),A=45°,则满足此条件的三角形个数是( )
A.0
B.1
C.2
D.无数个
查看答案