命题“若a=0且b=0,则a2+b2=0”的否命题为 .
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在△ABC,设角A,B,C的对边分别为a,b,c,且
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=
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,则角B=
.
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若直线2ax-by+2=0(a>0,b>0)被圆x
2+y
2+2x-4y+1=0截得的弦长为4,则
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+
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的最小值为
.
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已知实数m是2,8的等比中项,则圆锥曲线
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=1的离心率为
.
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设双曲线
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的虚轴长为2,焦距为
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103102301227608257/SYS201311031023012276082009_ST/1.png)
,则双曲线的渐近线方程为( )
A.
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B.y=±2
C.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103102301227608257/SYS201311031023012276082009_ST/3.png)
D.
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已知双曲线
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103102301227608257/SYS201311031023012276082008_ST/0.png)
,过其右焦点且垂直于实轴的直线与双曲线交于M,N两点,O为坐标原点.若OM⊥ON,则双曲线的离心率为( )
A.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103102301227608257/SYS201311031023012276082008_ST/1.png)
B.
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C.
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131103102301227608257/SYS201311031023012276082008_ST/3.png)
D.
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