All combination of the (x,y) values you have found are stationary points, i.e. (0,0), (0,-1), (3,0) and (3,-1).
Hi I'm having trouble with the critical points.
f(x,y) = 2x^3 + 2y^3 - 9x^2 + 3y^2 - 12
fx = 6x^2 - 18x
0 = 6x^2 - 18x
x = 0 and 3
fy = 6y^2 + 6y
0 = 6y^2 + 6y
y = 0 and -1
Here is where i get stuck. I'm not sure what values of y to use for the x intercepts.
Could anyone show me what the critcal points are.