If I have a system like:
$\frac{dx}{dt} = x, \frac{dy}{dt} = -y+x^2$
and I am asked to draw a phase portrait, once I have found the type of portrait (saddle point, node, spiral, etc.) from the eigenvalues and have found the $\infty$-isocline and $0$-isocline, how do I determine the direction of the arrows on the portrait?