I have to the function f(x,y)=1/2x

^{4}+3y

^{2}-6xy

I'm ought to find and classify stationary points.

I'm not sure if I went about this right, but i began assuming ∂f/∂y=0 and ∂f/∂x=0. I got two equations with two unknowns:

(1) 2x

^{3}-6y=0

(2) 6y-6x=0

Now I solved for x and y.

(1) y=x

^{3}/3

(2) y=x

From this point I'm not sure how to proceed to find and classify stationary points. Help much appreciated.