1. The problem statement, all variables and given/known data http://puu.sh/1QFsA [Broken] 2. Relevant equations 3. The attempt at a solution I'm actually not sure how to do this question. How do i find Δx^2. I kind of understand the question but I don't know how to prove it. I know that Δy becomes dy when the width becomes infinitesimally small (Ʃ (infinity)). And y'' is basically the second derivative... but I have no clue how to go about verifying this... This is my attempt: http://puu.sh/1QFqE [Broken] I, myself, think it looks more like gibberish. Could someone nudge me to the right direction, please? Thanks!