[25] Consider the system
\[ \dot {x}=x^2-xy \]
\[ \dot {y}=-y+x^2 \]
Determine the stability at the origin by constructing an approximate center manifold of the form \(y=ax^2+bx^3+\cdots \) and analyzing the flow on the approximate center manifold. Sketch the phase portrait showing the center and stable manifolds.