??????? Problem \( 4^{\star} \) : Show that the system \[ \begin{array}{l} \dot{x}=-y-x y^{2}+z^{2}-x^{3}, \\ \dot{y}=x+z^{3}-y^{3}, \\ \dot{z}=-x z-x^{2} z-y z^{2}-z^{5}, \end{array} \] is not a gradient sys 2 answers