Translations:Point of maximum depth/5/en

${\begin{aligned}e^{at_{D}}&{\rm {=}}{\frac {{\rm {\ tan\ }}{\frac {{\theta }_{D}}{\rm {2}}}}{{\rm {\ tan\ }}{\frac {{\theta }_{0}}{\rm {2}}}}}{\rm {=}}{\frac {{\rm {\ tan\ }}{\frac {\pi }{\rm {4}}}}{{\rm {\ tan\ }}{\frac {{\theta }_{0}}{\rm {2}}}}}{\rm {=}}{\frac {\rm {l}}{{\rm {\ tan\ }}{\frac {{\theta }_{0}}{\rm {2}}}}}{\rm {=}}{\frac {\rm {l}}{\frac {{\rm {1}}-{\rm {\ cos\ }}{\theta }_{0}}{{\rm {\ sin\ }}{\theta }_{0}}}}{\rm {=}}{\frac {{\rm {\ sin\ }}{\theta }_{0}}{{\rm {l}}-{\rm {\ cos\ }}{\theta }_{0}}},\end{aligned}}$

(57)