#### Answer

a) For all (x,y) except the lines $x=2$ and $x=1$
b) For all (x,y) except parabola $y=x^2$

#### Work Step by Step

a) There must not be zero in the denominator. After factoring the denominator into $(x-2)(x-1)$, we see that the function is defined for all $(x,y)$ except the lines $x=2$ and $x=1$
b) To avoid the denominator being zero, we make sure that $x^2-y\ne 0$ or $y\ne x^2$.