1. The problem statement, all variables and given/known data for the line segment c2 , why did the author want to differentiate dx with respect to dy ? and he gt dx = 0 ? I'm curious why did he didnt do so for C3 , where dy= 0 ..Why didnt he also differentiate dy with dx ? dy/dx = 0 ? 2. Relevant equations 3. The attempt at a solution is there anything wrong with the working ?