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在正三棱锥S-ABC中,M、N分别为棱SC、BC的中点,且MN⊥AM,SA=2,...
在正三棱锥S-ABC中,M、N分别为棱SC、BC的中点,且MN⊥AM,SA=2
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,则此三棱锥S-ABC外接球的表面积为
.
考点分析:
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设O为坐标原点,M(2,-1),点N(x,y)满足
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已知函数f(x)是在(0,+∞)上每一点处可导的函数,若xf′(x)-f(x)>0在x>0上恒成立,且f(x)=xa
x(a>0,a≠1,x>0),
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=
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,若数列{
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}(n∈N)的前n项和为S
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S
n=( )
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B.1
C.-2
D.-
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已知椭圆
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=1(a>b>0)的左、右焦点为F
1,F
2,P为椭圆上的一点,且|PF
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2|的最大值的取值范围是[2c
2,3c
2],其中c=
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.则椭圆的离心率的取值范围为( )
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]
B.[
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,1)
C.[
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,1)
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,
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若函数f(x)=log
a(2x
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C.
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D.(0,+∞)
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