Cos(a+b)+sin a* sin b/sin(a-b)-sin a *cos b

Question

Cos(a+b)+sin a* sin b/sin(a-b)-sin a *cos b

Answer 1

(cosacosb-sina-sinb=sinasinb)/(sinacosb-sinbcosa-sinacosb)=
=cosacosb/(-sinbcosa)=-cosb/sinb=-ctgb