Question Number 2355 by 123456 last updated on 17/Nov/15
$$\frac{{df}}{{d}\zeta}\mathrm{sinh}\:\zeta+\frac{{df}}{{d}\theta}\mathrm{sin}\:\theta+\frac{{df}}{{d}\rho}\rho=\mathrm{0} \\ $$$${f}\left(\rho,\zeta,\theta\right)=?? \\ $$
df-d-sinh-df-d-sin-df-d-0-f-