A charge of 0.883 nC is placed at the origin. Another charge of 0.347 nC is placed at x1 = 13.1 cm on the x-axis. At which point on the x-axis does this potential have a minimum? I do know a few things: A necessary condition for the potential to have a minimum is that its derivative is 0. The minimum is between the two charges. I need to take the derivative of: k*q1/r - k*q2/(r-x1), but I'm not sure about how to go about that? I'm not looking for the answer. Just need some help setting this up.