#### Answer

a) For all (x,y,z)
b) For all (x,y,z) except the interior of the cylinder $x^2+y^2=1$

#### Work Step by Step

a) Since there are no fractions or square roots, all values are allowed.
b) We must make sure that the radical does not contain a negative: $x^2+y^2-1\ge 0$. Thus $x^2+y^2\ge 1$ (points outside the cylinder or on its surface).