Let f : R2 > R be defined by f(x,y) = x4 y3 2x2 + By a) Find the critical point of f, and identify them as a local minimum, maximum, and saddle points. b) Let S be the region in the xyplane that lies inside the pentagon with vertices at (0,1.5), (0,1), (1,1), (15,0) and (15,-1.5). Find the global maximum and minimum values of f on S and the points at which they occur. Mark these points in a sketch of S