Describe the domain of \( f \) in words.
(a) \( f(x, y)=x e^{-\sqrt{y+2}} \)
(b) \( f(x, y, z)=\sqrt{25-x^{2}-y^{2}-z^{2}} \)
(c) \( f(x, y, z)=e^{x y z} \)
(a) \( f(x, y)=\frac{\sqrt{4-x^{2}}}{y^{2}+3} \)
(b) \( f(x, y)=\ln (y-2 x) \)
(c) \( f(x, y, z)=\frac{x y z}{x+y+z} \)
