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