ABSTRACT
The formalism of the method of averaging for investigating resonant solutions in systems with slowly varying coefficients was evolved by Mitropolskii [1964]. Periodic perturbations of two-dimensional systems with a rapidly rotating phase and slowly varying coefficients were considered by Morrison [1968]. He deduced equations of the second approximation and obtained the conditions for the closeness of solutions of the exact and averaged equations on a finite asymptotically large time interval.
