I am currently learning 3D functions and their graphs.
I know that, for 2D graphs, a function $y=f(x)$ would have either a maxima or a minima at $(x,y)$ for,
$$\frac{dy}{dx}=0$$
Is there a similar way to find out where a 3D surface $z=f(x,y)$ has it's maxima and minima?