Tunc, Cemil2025-05-102025-05-1020101521-1398https://hdl.handle.net/20.500.14720/17034In this paper, we are concerned with the existence of periodic Solutions to nonlinear third order delay differential equation: x'''(t) + psi(x'(t))x('')(t) + g(x'(t - r)) + f(x(t)) = p(t, x(t), x(t - r), x'(t), x'(t - r), x ''(t)), when p(t, x(t), x(t - r), x'(t), x'(t - r), x ''(t)) is a periodic function of period T, T > 0. With use of Lyapunov's functional approach, we establish some new sufficient conditions which guarantee that there exists a periodic solution of this equation of period T, T > 0. For illustrations, an example is also given on the existence of periodic solutions.eninfo:eu-repo/semantics/closedAccessPeriodic SolutionsNonlinear Differential Equations With DelayThird OrderArticle