Question

【急在线等】tana/(tana-1)=-1,求（1）(sina-3cosa)/(sina+cosa).(2).sin^

Answer 1

tana/(tana-1)=-1,有tana=1/2,tan2a=2tana/(1-tana^2 )=4/3,

sin2a=4/5,cosa=3/5;

或sin2a=-4/5,cosa=-3/5;

(1)）(sina-3cosa)/(sina+cosa)=(tana-3)/(tana+1)(分子分母同时除以cosa)

=-5/3

(2))sin^2 a+sinacosa=(1-cos2a)/2+sin2a/2=3/5或2/5