2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/112677For a class of polynomial non-autonomous differential equations of degree n, we use phase plane analysis to show that each equation in this class has n periodic solutions. The result implies that certain rigid two-dimensional systems have at most one limit cycle which appears through multiple Hopf bifurcation.Classical Analysis and ODEsDynamical Systems34Ctext