Thomas' Calculus 13th Edition

a. Domain : The set of all $(x,y)\ne (0,y)$ b. Range: Real numbers c. Level Curves: The level curves are the x-axis minus origin when $f(x,y)= 0$ and the parabolas $y=cx^2$ minus origin for $f(x,y)=c \ne 0$ d. Boundary point is the line $x=0$ e. Open only f. Unbounded