∃x∈Q,x2=3的否定是 .
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在实数集上定义运算⊗:x⊗y=x(1-y),若不等式(x-a)⊗(x+a)<1对任意实数x都成立,则实数a的取值范围是( )
A.(-1,1)
B.(0,2)
C.
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D.
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已知△ABC中,sinA:sinB:sinC=k:(k+1):2k (k≠0),则k的取值范围为( )
A.(2,+∞)
B.(0,2)
C.(
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,2)
D.(
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,+∞)
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目标函数z=2x+y,变量x,y满足
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,则有( )
A.z
max=12,z
min=3
B.z
max=12,z无最小值
C.z
min=3,z无最大值
D.z既无最大值,也无最小值
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等差数列{a
n}的前m项和为30,前2m项和为100,则它的前3m项和为( )
A.130
B.170
C.210
D.260
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下列结论正确的是( )
A.当x>0且x≠1时,lgx+
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B.当x≥2时,
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的最小值为2
C.当0<x≤2时,
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无最大值
D.当x>0时,
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