(sina/cosa+sinb/cosb)/(sina/cosa-sinb/cosb)=(sin(a+b)/cosacosb)/(sin(a-b)/cosacosb)=sin(a+b)/sin(a-b)
(sina/cosa+sinb/cosb)/(sina/cosa-sinb/cosb)=(sin(a+b)/cosacosb)/(sin(a-b)/cosacosb)=sin(a+b)/sin(a-b)