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某学校高一、高二、高三共有2400名学生,为了调查学生的课余学习情况,拟采用分层...
某学校高一、高二、高三共有2400名学生,为了调查学生的课余学习情况,拟采用分层抽样的方法抽取一个容量为120的样本.已知高一有760名学生,高二有840名学生,则在该学校的高三应抽取 名学生.
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在(2x-
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)
4的二项展开式中,常数项是8,则a的值为
.
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若
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=a+bi(a,b∈R),则a-b的值是
.
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在△ABC中,已知
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•
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=9,sinB=cosA•sinC,S
△ABC=6,P为线段AB上的点,且
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=x
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+y
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,则xy的最大值为( )
A.1
B.2
C.3
D.4
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已知点P是双曲线C:
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左支上一点,F
1,F
2是双曲线的左、右两个焦点,且PF
1⊥PF
2,PF
2与两条渐近线相交于M,N两点(如图),点N恰好平分线段PF
2,则双曲线的离心率是( )
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A.
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B.2
C.
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D.
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设不等式组
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表示的平面区域为D.若圆C:(x+1)
2+(y+1)
2=r
2(r>0)不经过区域D上的点,则r的取值范围是( )
A.[2
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,2
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]
B.(2
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,3
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C.(3
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,2
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]
D.(0,2
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)∪(2
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,+∞)
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