Chapter 13.8, Problem 22ES

Use a CAS to generate a contour plot of

$f\left(x,y\right)=2y^{2}x-y{x}^2+4xy\text{for}-5\le x\le 5\text{and}-5\le y\le 5,$ and use the plot to ap-proximate the locations of all relative extrema and saddle points in the region. Check your answer using calculus, and identify the extrema as relative maxima or minima.