Chapter 6, Problem 6.5P

I have been able to do this with derivatives but I can't figure out how to do this with definite integrals

Consider a satellite in elliptical orbit around a planet of mass M, and suppose that physical units are so chosen that GM D 1 (where G is the gravitational constant). If the planet is located at the origin in the xy-plane, then Explain the equations of motion of the satellite? Let T denote the period of revolution of the satellite. Kepler’s third law says that the square of T is proportional to the cube of the major semiaxis a of its elliptical orbit. In particular, if GM D 1, then?

Consider the Lennard-Jones potential between atoms in a solid material. Find the dependence of the equilibrium postion x0, on the parameters in the potential. Then for small perturbations, δx around x0, determine the restoring force as a function of δx.