Suppose, I have a function like this : $f(x,y)=5x+\sqrt{y}$
Simply what I do that is find $z$ axis for each possible numbers.
$$f(0,0)$$ $$f(0,1)$$ $$f(1,0)$$
But, it becomes very "hard" to find the axis and it takes lot of time to graph it. Actually, how a professional finds axis? I would like to find the graph without calculator (How professional graph it without calculator?).
Look how hard the following graph is
