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已知空间四边形ABCD的各边及对角线相等,AC与平面BCD所成角的余弦值是 .
已知空间四边形ABCD的各边及对角线相等,AC与平面BCD所成角的余弦值是 .
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已知直线
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交椭圆x
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A.
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B.
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C.
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D.
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直线
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与椭圆
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相交于A,B两点,该椭圆上点P,使得△PAB面积等于3,这样的点P共有( )
A.1个
B.2个
C.3个
D.4个
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若双曲线x
2-y
2=1的右支上一点P(a,b)到直线y=x的距离为
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,则a+b的值为( )
A.-
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B.
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C.±
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D.±2
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