设a为第四象限角,若sin3a/sina+13/5,则tana=

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设a为第四象限角,若sin3a/sina+13/5,则tana=
设a为第四象限角,若sin3a/sina+13/5,则tana=

设a为第四象限角,若sin3a/sina+13/5,则tana=
sin3A/sinA=(sin2AcosA+cos2AsinA)/(sin2AcosA-cos2AsinA)=13/5
5sin2A+5cos2AsinA=13sin2AcosA-13cos2AsinA
8*2sinAcosA*cosA=18cos2AsinA
8cosA*cosA=9cosA*cosA-9sinA*sinA
tanA=-1/3(A为第四象限角,tanA小于0)
tan2A=2tan2A/(1-tanA*tanA)=-3/4