1. The problem statement, all variables and given/known data Given a semi-infinite stick (that is, one that goes off to infinity in one direction), determine how its density should depend on position so that it has the following property: If the stick is cut at an arbitrary location, the remaining semi-infinite piece will balance on a support that is located a distance l from the end. http://www.personal.kent.edu/~fwilliam/Chapter 1 Statics.pdf - Problem 18 2. Relevant equations T = r x F 3. The attempt at a solution In the linked solution, I understand the setup, but I do not understand how to find the derivative of the integral with respect to x0. Can someone give me a more detailed explanation of this step?