2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/226743We show that the Lindstedt-Poincare perturbation theory is always a reliable technique in the region of small coupling constant. The harmonic balance result, on the other hand, if expanded in the perturbation parameter may lead to incorrect results.15 pages, 1 figureChaotic Dynamicstext