Question

a

Answer 1

Yeah. X and y can be any real number(s). No restrictions.

Answer 2

I don't see why not. The domain of the cosine function is unrestricted, and x^2 - y^2 can produce any real number.

Answer 3

It's the domain of the entire function, not just the individual sets for x and y. You can assume that x and y are elements of R, but that is not the question.

Answer 4

Yeah, I think that works fine.