I also have a question on the directional direvatives at the origin and whether or not they exist. For the partial direvative of x at the origin I got 0 and same for partial of y.

So I was using Duf(0,0) =fx cos() + fy sin() to find, but since both my fx and fy are 0 all I get is 0.

Is it possible that I got the right answer in that Duf(0,0) = 0?

Please help.

Thanks