Given is the function f: R2 -> R, with f(x,y)=x2+y2-6xy+8y.
The level surface f(x,y)=1 contains infinitely much points (x,y) where x and y
are integer.
How can I prove this?
I see that it is true with some examples, but how can I prove this.
Do I need to use the gradient? Or tangent planes? Or...