Synchronous machines and grid-following converters exhibit nonlinear second-order differential equations that rule their synchronization dynamics. Furthermore, the attraction exerted by the stable equilibrium points is limited to a certain region of attraction. In small networks, where a single generator is connected to an infinite bus, the region of attraction is bounded by curves, and can be plotted in a plane. Hence, this paper presents a simplified version of the reverse trajectory method for identifying the region of attraction of an equilibrium point. The selection of the initial conditions is backed with physical arguments, and the performance of the method is tested with different parameters. A three-phase short circuit is also tested to verify the consistency of the boundaries obtained with this technique.