若a满足(sina-2cosa)/(sina+3c - 知识问答

若a满足(sina-2cosa)/(sina+3cosa)=2,则sina·cosa=

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上下同除以cosa
(tana-2)/(tana+3)=2
tana-2=2tana+6
tana=-8
sinacosa
=sinacosa/(sin²a+cos²a)
=1/[(sin²a+cos²a)/sinacosa)]
=1/(sina/cosa+cosa/sina)
=1/(tana+1/tana)
tana=-8
代入即可

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