To evaluate [tex](g \circ f)(0)[/tex], you'd start by rewriting this as [tex](g \circ f)(0) = g\big(f(0)\big)[/tex] and your first step of evaluation is to evaluate [tex]f(0)[/tex].
When you evaluate [tex]f(0)[/tex], you have the following:
[tex]f(0) = \dfrac{1}{0}[/tex]
and this is undefined. Since you cannot perform the first step of the evaluation, you cannot evaluate [tex](g\circ f)(0)[/tex].
