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数列{an}的前n项和sn=2an-3(n∈N*),则a5= .
数列{an}的前n项和sn=2an-3(n∈N*),则a5= .
考点分析:
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设F
1和F
2为双曲线
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=1(a>0,b>0)的两个焦点,若F
1,F
2,P(0,2b)是正三角形的三个顶点,则双曲线的离心率为( )
A.
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B.2
C.
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D.3
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下列有关命题的说法正确的是( )
A.命题“若x
2=1,则x=1”的否命题为:“若x
2=1,则x≠1”
B.“x=-1”是“x
2-5x-6=0”的必要不充分条件
C.命题“∃x∈R,使得x
2+x+1<0”的否定是:“∀x∈R,均有x
2+x+1<0”
D.命题“若x=y,则sinx=siny”的逆否命题为真命题
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已知(3,1)和(-4,6)在直线3x-2y+a=0的两侧,则a的取值范围是( )
A.a<1或a>24
B.a=7或a=24
C.-7<a<24
D.-24<a<7
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若b为实数,且a+b=2,则3
a+3
b的最小值为( )
A.18
B.6
C.2
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D.2
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在等比数列{a
n}中,若a
1=1,公比q=2,则a
12+a
22+…+a
n2=( )
A.(2
n-1)
2B.
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(2
n-1)
C.4
n-1
D.
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(4
n-1)
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