Hello, Im not sure how to set up this integral. Its a little more advanced than I am used too. Any ideas? Consider a thin ring of radius a and mass M. A mass m is placed in the plane of the ring (not in the center!). Determine the gravitational potential for r < a. Find a position of equilibrium and determine whether it is stable or unstable. (Hint: Consider a small displacement from the equilibrium position and do an expansion.) I think I have to use the law of cosines. But why would I need to do an expansion?