I have came up with a solution for this - in order for this function to be defined, we must have an x and y between negative infinity up to and including the number 1. If asked to graph this domain, does the domain lie on the x-y plane of three dimensional space, and is it the intersection of the domains of x and y? I know the only sensible way to my question will likely go over my head - I Just started vector calculus - so no worries, I find it difficult for this to make sense to me. I am thinking of the domain as the values "under" the z-plane in 3d space, if that makes any sense... at all - or above! or maybe a point in three-d space is ON the plane, when z is zero?