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专业文档珍贵文档1.12-sin215°的值是()A.64B.6-24C.32D.34解析:原式=12-1-cos2×15°2=cos30°2=34.答案:D2.已知sinθ=45,sinθcosθ0,则sin2θ的值为()A.-2425B.-1225C.-45D.2425解析:∵sinθ=450,sinθcosθ0,∴cosθ0.∴cosθ=-1-sin2θ=-35.∴sin2θ=2sinθcosθ=-2425.答案:A3.tanπ81-tan2π8=________.解析:原式=12×2tanπ81-tan2π8=12tan(2×π8)专业文档珍贵文档=12tanπ4=12.答案:124.在△ABC中,cosA=513,则sin2A=________.解析:∵0Aπ,∴sinA=1-cos2A=1213.∴sin2A=2sinAcosA=120169.答案:1201695.已知cosα=-1213,α∈(π,3π2),求sin2α,cos2α,tan2α的值.解:∵cosα=-1213,α∈(π,3π2),∴sinα=-1-cos2α=-1--12132=-513.∴sin2α=2sinαcosα=2×(-513)×(-1213)=120169,cos2α=1-2sin2α=1-2×(-513)2=119169,tan2α=sin2αcos2α=120119.
本文标题:【红对勾】人教版高中数学必修4练习手册:3-1-3二倍角的正弦、余弦、正切公式[-高考]
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