Iranian Mathematical Society (IMS)Bulletin of the Iranian Mathematical Society1017-060X41220150401Periodic solutions of fourth-order delay differential equation307314610ENS.BalamuralitharanSRM UNIVERSITY,Journal Article20131228In this paper the periodic solutions of fourth order delay differential equation of the form $\ddddot{x}(t)+a\dddot{x}(t)+f(\ddot{x}(t-\tau(t)))+g(\dot{x}(t-\tau(t)))+h({x}(t-\tau(t)))=p(t)$ is investigated. Some new positive periodic criteria are given. <br /> http://bims.iranjournals.ir/article_610_0669d6cfade607a09955798000b786fb.pdf