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下列四个命题中,真命题个数是 ①若“x+y=0,则x,y互为相反数”的逆命题②“...
下列四个命题中,真命题个数是
①若“x+y=0,则x,y互为相反数”的逆命题②“全等三角形的面积相等”的否命题
③若“q≤1,则x2+2x+q=0的有实根”的命题④“等边三角形的三个内角相等”的逆否命题( )
A.1
B.2
C.3
D.4
考点分析:
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已知△ABC的顶点B、C在椭圆
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上,顶点A是椭圆的一个焦点,且椭圆的另外一个焦点在BC边上,则△ABC的周长是( )
A.
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B.6
C.
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D.12
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有四个关于三角函数的命题:
P
1:∃x∈R,sin
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+cos
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=
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;
P
2:∃x、y∈R,sin(x-y)=sinx-siny;
P
3:∀x∈[0,π],
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=sinx;
P
4:sinx=cosy⇒x+y=
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.
其中假命题的是( )
A.P
1,P
4B.P
2,P
4C.P
1,P
3D.P
2,P
4
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”m>n>0”是”方程mx
2+ny
2=1表示焦点在y轴上的椭圆”的( )
A.充分而不必要条件
B.必要而不充分条件
C.充要条件
D.既不充分也不必要条件
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设等比数列{a
n}的前n项和为S
n,若
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=3,则
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=( )
A.2
B.
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C.
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D.3
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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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≥2
B.当x>0时,
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+
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≥2
C.当x≥2时,x+
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的最小值为2
D.当0<x≤2时,x-
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无最大值
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