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设等差数列{an}的公差d≠0,a1=4d.ak是a1与a2k的等比中项,则k=...
设等差数列{an}的公差d≠0,a1=4d.ak是a1与a2k的等比中项,则k=( )
A.3或-1
B.3或1
C.3
D.1
考点分析:
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、
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的夹角为60°,则
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=(
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,1),|
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|=1,则|
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|═( )
A.2
B.
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C.2
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D.2
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的展开式中常数项是( )
A.-160
B.-20
C.20
D.160
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已知集合U=R,A={x|x
2-5x+6≥0},那么∁
UA=( )
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B.{x|2<x<3}
C.{x|x≤2或x≥3}
D.{x|2≤x≤3}
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对于n∈N
*(n≥2),定义一个如下数阵:
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,其中对任意的1≤i≤n,1≤j≤n,当i能整除j时,a
ij=1;当i不能整除j时,a
ij=0.设
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.
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66并计算
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;
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;
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,求证:g(n)-1<f(n)<g(n)+1.
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已知椭圆
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,且椭圆上的点到两个焦点的距离和为2
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