在三棱锥A-BCD中,AD⊥面BCD,BD⊥CD,AD=BD=2,
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,E、F分别是AC和BC的中点.
(1)求三棱锥E-CDF的体积;
(2)求二面角E-DF-C的大小(用反三角函数值表示).
考点分析:
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1=z
2.
(1)求α的值;
(2)设t=cosα+isinα,求f(t)=1+t+t
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n-1(n∈N*).
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已知函数
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B.(2,5)
C.(3,6)
D.(4,8)
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已知M是△ABC内的一点,且
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=2
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抛物线y=x
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,0)
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C.(0,
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)
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D.既非充分又非必要条件
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