题目内容
化简:4cos(60°-θ)·cosθ·cos(60°+θ).解:4cos(60°-θ)·cosθ·cos(60°+θ)
=2cosθ·［cos120°+cos(-2θ)］
=-cosθ+2cosθ·cos(-2θ)
=-cosθ+cos3θ+cosθ
=cos3θ.
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题目内容
化简:4cos(60°-θ)·cosθ·cos(60°+θ).解:4cos(60°-θ)·cosθ·cos(60°+θ)
=2cosθ·［cos120°+cos(-2θ)］
=-cosθ+2cosθ·cos(-2θ)
=-cosθ+cos3θ+cosθ
=cos3θ.