## Thomas' Calculus 13th Edition

a. Domain : This is the set of all points lie in the xy -plane. b. Range: A set of all Real numbers c. Level Curves: These are $f(x,y)=0 \rightarrow y \pm x$ and for $f(x,y)=c\ne 0$. These are the hyperbolas having center (0,0) and focus on the x-axis when $c\gt 0$ as well as the other at the y-axis when $c \lt 0$ d. No Boundary points e. Both Open and Closed f. Unbounded