FAN, J. Application of He’s frequency-amplitude formulation to the Duffing-harmonic oscillator. Topological Methods in Nonlinear Analysis, [S. l.], v. 31, n. 2, p. 389–394, 2008. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2008.031. Acesso em: 27 apr. 2024.