\[
\boxed{
 \left\{ {\frac {{\rm d}^{2}}{{\rm d}{t}^{2}}}x \left( t \right) = \left( 3\, \left( \cos \left( at+b \right)  \right) ^{2}-1 \right) {c}^{2}x \left( t \right) +3/2\,{c}^{2}y \left( t \right) \sin \left( 2\,atb \right) ,{\frac {{\rm d}^{2}}{{\rm d}{t}^{2}}}y \left( t \right) = \left( 3\, \left( \sin \left( at+b \right)  \right) ^{2}-1 \right) {c}^{2}y \left( t \right) +3/2\,{c}^{2}x \left( t \right) \sin \left( 2\,atb \right)  \right\} }
\]