number systems/signing

Hi /prog/

How does one represent negative numbers in hex/octal, e.g -15. Would the hex value be F1 or -0F? In the example i've been given it says -15 is F1, but I dont see how the sign is represented, shouldn't F1 be +241?

>>6
No, you fuck off you mental midget. We have a few production level servers here at work that use 1's complement. Now shut up and go scrub another toilet.