Periodic solutions for a second order nonlinear functional differential equation Original Research Article

The second order nonlinear delay differential equation with periodic coefficients View the MathML sourcex″(t)+p(t)x′(t)+q(t)x(t)=r(t)x′(t−τ(t))+f(t,x(t),x(t−τ(t))),t∈R Turn MathJax on is considered in this work. By using Krasnoselskii’s fixed point theorem and the contraction mapping principle, we establish some criteria for the existence and uniqueness of periodic solutions to the delay differential equation.