Chapter 13.1, Problem 3QCE

Let $f(x,y)=e^{x+y}.$

(a) For what values of k will the graph of the level curve $f\left(x,y\right)=k$ be nonempty?

(b) Describe the level curves $f\left(x,y\right)=k$ for the values of k obtained in part (a).