(sina+cosa)/(sina-cosa)=3
上下同除以cosa且tana=sina/cosa
(tana+1)/(tana-1)=3
tana+1=3tana-3
tana=2
tan(b-2a)
=-tan(2a-b)
=-tan(a-b+a)
=-[tan(a-b)+tana]/[1-tan(a-b)*tana]
=-(2+2)/(1-2*2)
=4/3
(sina+cosa)/(sina-cosa)=3
上下同除以cosa且tana=sina/cosa
(tana+1)/(tana-1)=3
tana+1=3tana-3
tana=2
tan(b-2a)
=-tan(2a-b)
=-tan(a-b+a)
=-[tan(a-b)+tana]/[1-tan(a-b)*tana]
=-(2+2)/(1-2*2)
=4/3