\[
\boxed{
 \left\{ {\frac {\rm d}{{\rm d}t}}x \left( t \right) = \left( y \left( t \right)  \right) ^{2}-\cos \left( x \left( t \right)  \right) ,{\frac {\rm d}{{\rm d}t}}y \left( t \right) =-y \left( t \right) \sin \left( x \left( t \right)  \right)  \right\} }
\]