\qquad {EF \over {FA}} \cdot  {FA \over{FB}} \cdot  {FB \over {FD}}=\cot {(\omega +10^o)} \cdot \cot \omega \cdot \cot {(\omega -10^o)} \iff  {EF \over {FD}}= \cot {(\omega +10^o)} \cdot \cot \omega \cdot \cot {(\omega -10^o)} \iff