a属于（0,pai ）,sina+cosa=7/13,tana=?

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sina+cosa=7/13,
(sina+cosa)^2=1+2sinacosa=49/169
sinacosa=-60/169
sinacosa/1=sinacosa/(sin^2a+cos^2a)=tana/(1+tan^2a)=-60/169
60tan^2a+169tana+60=0
(12tana+5)(5tana+12)=0
tana=-5/12,tana=-12/5