I would to make this substitution with 2 rules. Nothing is happening.
(Sin[η2] ((Cos[θ2]* Cos[ψ1])/Sin[ψ1] + Cos[ψ2] Sin[θ2]) == Cos[η2] Sin[ψ2]) /. Sin[ψ1] -> (Cos[ϕ2] Sin[η2])/Sin[ψ2] /. Cos[ψ1] -> Cos[η2] Cos[θ2] Cos[ϕ2] - Sin[θ2] Sin[ϕ2]
Have you an idea why i didn't manage to make these substitutions ? Sorry if my question is may be very simple, but i blocked.