Hopefully easy question about sups of continuous functions

AxiomOfChoice

If f is a continuous functional on a normed space, do you have

[tex]
\sup_{\|x\| < 1} |f(x)| = \sup_{\|x\| = 1} |f(x)|
[/tex]

If so, why? If not, can someone provide a counterexample?

Stephen Tashi

That's an interesting question. A normed space must be a vector space right? But does a vector space have to be connected?

mathwonk

try it on R. can you think of a function which gets larger somewhere inside the unit interval than it is at 1, -1? maybe you meant linear. or maybe functional means linear. then it seems true.

AxiomOfChoice

Yeah, I did mean to put "linear functional" above...I guess I was under the impression that "functional" implies "linear functional", though I'm not at all sure that's the case.

And yeah, it clearly seems true on R, but for an arbitrary normed space, I'm not so sure...