\[
\boxed{
{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left( x \right) + \left( {\frac {\rm d}{{\rm d}x}}y \left( x \right)  \right) \tan \left( x \right) +y \left( x \right)  \left( \cos \left( x \right)  \right) ^{2}=0}
\]