1. The problem statement, all variables and given/known data Prove that the function [tex]f(x)=\sqrt(1-\sqrt(1-x^2))[/tex] has a finite one sided derivative at the point x=0. 2. Relevant equations 3. The attempt at a solution What the heck is a one sided derivative? If I differentiate it, and put limit x=0, I get infinity, which is definately NOT finite! Do I use the fundamental definition of a derivative here and put lim x=0- or something?