Chapter 13.1, Problem 47ES

In each part, match the contour plot with one of the functions

$\begin{array}{l}f(x,y)=\sqrt{x^2+y^2},f(x,y)=x^2+y^2,\\ f(x,y)=1-x^2-y^2\end{array}$

by inspection, and explain your reasoning. Larger values of z are indicated by lighter colors in the contour plot, and the concentric contours correspond to equally spaced values of z.