1. The problem statement, all variables and given/known data I want to show that if the chhord length ||f(s)-f(t)|| depends only on |s-t| then the f is part of a line or circlle. f may not be regular or unit speed. 2. Relevant equations 3. The attempt at a solution I'm trying to differentiete it and taking ||f'(t)||, but I really need help, because it's not working for me.