Answer
a) for all (x,y) except $y=x$ b) for all (x,y)
Work Step by Step
a) There can be no zero in the denominator. Thus, for all $(x,y)$ except $y=x$
b) Here, the square of the denominator is not negative. Thus, for all (x,y)
Hence, our answers are: a) for all (x,y) except $y=x$ b) for all (x,y)
