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设向量=(1.cosθ)与=(-1,2cosθ)垂直,则cos2θ等于 ( ) ...
设向量
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=(1.cosθ)与
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=(-1,2cosθ)垂直,则cos2θ等于 ( )
A.
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B.
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C.0
D.-1
考点分析:
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A.-sin2
B.-1
C.
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D.1
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化简
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,sinβ=
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B.
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或
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(I)求函数f(x)的最小值;
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