If $f:A\rightarrow B$ is continuous, A is a compact set of some metric $Y$, how dows one show $||f||$ is continuous, ...if it even is continuous. I am inducing that it is since if a real functions is continuous, then its absolute value function is as well.
Using the triangle inequality, you have $||x|| \leq ||x-y|| + ||y||$, and similarly with $x,y$ reversed. From this you can conclude that $|\;||x||-||y||\;| \leq ||x-y||$, ie, the norm is continuous. Now apply this, replacing $x$ by $f(x)$ and $y$ by $f(y)$, and use continuity of $f$.