Domain of a function in two variables

Hello MHF,

Have this question, and I am really unsure about function in multiple variables..

Find the domain of each of the following functions and sketch it, showing clearly whether any parts of the boundary are included in the domain

(a)

(b)

So for equation (a) obviously which I have reduced to so that i can graph it, and the boundry of the graph is included in the domain.

For part (b) it is similiar because isn't defined, so , so this can be reduced to so that it can be graphed, and the boundry of the graph isn't in the domain?