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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....
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°
考点分析:
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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)
∥
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,
![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
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873003_ST/0.png)
和
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873003_ST/1.png)
.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'=( )
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873003_ST/images2.png)
A.4
B.6
C.8
D.9
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已知空间直角坐标系中A(1,1,0)且
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873002_ST/0.png)
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)
查看答案
一质点受到平面上的三个力F
1,F
2,F
3(单位:牛顿)的作用而处于平衡状态.已知F
1,F
2成60°角,且F
1,F
2的大小分别为2和4,则F
3的大小为( )
A.6
B.2
C.2
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123733327787366/SYS201310251237333277873001_ST/0.png)
D.2
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