a属于（0,pai）sina+cosa=7/13,tan=?

a属于（0,pai）sina+cosa=7/13,tan=?
a属于（0,pai）sina+cosa=7/13,tan=?

a属于（0,pai）sina+cosa=7/13,tan=?
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