a属于(0,pai ),sina+cosa=7/13,tana=?

问题描述:

a属于(0,pai ),sina+cosa=7/13,tana=?

sina+cosa=7/13,(sina+cosa)^2=1+2sinacosa=49/169sinacosa=-60/169sinacosa/1=sinacosa/(sin^2a+cos^2a)=tana/(1+tan^2a)=-60/16960tan^2a+169tana+60=0 (12tana+5)(5tana+12)=0tana=-5/12,tana=-12/5