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在正四面体ABCD的面上,到棱AB以及C、D两点的距离都相等的点共有( ) A....
在正四面体ABCD的面上,到棱AB以及C、D两点的距离都相等的点共有( )
A.1个
B.2个
C.3个
D.4个
考点分析:
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正四棱锥的侧棱长与底面边长都是1,则侧棱与底面所成的角为( )
A.75°
B.60°
C.45°
D.30°
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向量
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/0.png)
=(-2,-3,1),
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/1.png)
=(2,0,4),
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/2.png)
=(-4,-6,2),下列结论正确的是( )
A.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/3.png)
∥
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/4.png)
,
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/5.png)
⊥
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/6.png)
B.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/7.png)
∥
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/8.png)
,
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/9.png)
⊥
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/10.png)
C.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/11.png)
∥
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/12.png)
,
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/13.png)
⊥
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873005_ST/14.png)
D.以上都不对
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在正三棱锥P-ABC(顶点在底面的射影是底面正三角形的中心)中,AB=4,PA=8,过A作与PB,PC分别交于D和E的截面,则截面△ADE的周长的最小值是( )
A.9
B.10
C.11
D.12
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如图,平面α⊥平面β,A∈α,B∈β,AB与两平面α、β所成的角分别为
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和
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.过A、B分别作两平面交线的垂线,垂足为A'、B',若AB=12,则A'B'=( )
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A.4
B.6
C.8
D.9
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AB=(4,0,2),则B点坐标为( )
A.(9,1,4)
B.(9,-1,-4)
C.(8,-1,-4)
D.(8,1,4)
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