## Calculus: Early Transcendentals 8th Edition

a) A function is considered to be written as $f(x,y)$ with two variables $x,y$ in a set of domain D of real numbers. b) The three methods for visualizing a function of two variables are given below: i) A function $f(x,y)$ can be visualized by graphing it. ii) A contour map is the best method for visualizing a function of two variables. It consists of level surfaces such as $f(x,y)=p$ (p=a constant term). These are horizontal traces of the graph of the function which shows the projection onto the $xy$ plane. iii) The third method is an arrow vector diagram.