\[
\boxed{
{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left( x \right) ={\frac { \left( 3\, \left( \sin \left( x \right)  \right) ^{2}+1 \right) {\frac {\rm d}{{\rm d}x}}y \left( x \right) }{\cos \left( x \right) \sin \left( x \right) }}+{\frac {y \left( x \right)  \left( \sin \left( x \right)  \right) ^{2}}{ \left( \cos \left( x \right)  \right) ^{2}}}=0}
\]