Sharif University of Technology Scientia Iranica 1026-3098 15 2 2008 04 01 On the Existence of Periodic Solutions for Nonlinear Ordinary Di erential Equations 2968 EN D. Shadman Department of Mathematical Sciences,Sharif University of Technology B. Mehri Department of Mathematics,Sharif University of Technology Journal Article 2009 05 30 In this paper, the existence of periodic solutions of autonomous ordinary di erential equations of a 4th and 5th order is investigated. The method used is based on the Brower's degree theorem using the homotopy invariant a property of a topological degree. https://scientiairanica.sharif.edu/article_2968_62da8c91ce7b10846231921795d6059e.pdf