Existence nonexistence and multiplicity of periodic solutions for a kind of functional differential equation with parameter

In this paper, we study the existence, multiplicity and nonexistence of positive ωω-periodic solutions for a kind of second-order delay functional differential equation with parameter ü(t)+a(t)u(t)=λf(t,u(t−τ0(t)),u(t−τ1(t)),…,u(t−τn(t))) by employing the Krasnoselskii fixed point theorem for a cone map, where λ>0λ>0 is a parameter; some new results are obtained. As an application of our results, we discuss an example.