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倍角公式:
sin(2α)=2sinα·cosα=2/(tanα cotα)
cos(2α)=cos^2(α)-sin^2(α)=2cos^2(α)-1=1-2sin^2(α)
tan(2α)=2tanα/[1-tan^2(α)]
三倍角公式:
sin(3α)=3sinα-4sin^3(α)
cos(3α)=4cos^3(α)-3cosα
半角公式:
sin(α/2)=±√((1-cosα)/2)
cos(α/2)=±√((1 cosα)/2)
tan(α/2)=±√((1-cosα)/(1 cosα))=sinα/(1 cosα)=(1-cosα)/sinα
降幂公式
sin^2(α)=(1-cos(2α))/2=versin(2α)/2
cos^2(α)=(1 cos(2α))/2=vercos(2α)/2
tan^2(α)=(1-cos(2α))/(1 cos(2α))
万能公式:
sinα=2tan(α/2)/[1 tan^2(α/2)]
cosα=[1-tan^2(α/2)]/[1 tan^2(α/2)]