Criteria for the Existence of a Sustainable Limit Cycle. Application of the Criteria in the First Approximation for the Van der Pol Equation

The article proposes two criteria that the energy meets in order for the second-order differential equation to have a limit cycle and to be stable. The criteria were applied to establish the presence and stability of a limit cycle for the Van der Pol equation. Questions have been asked to be clarified using the method presented.