Positive, negative and mixed-type solutions for periodic vector differential equations

Abstract

This paper is devoted to the study of periodic solutions of the first-order vector differential equations $x'(t)+f(t,x(t))=0$. We first introduce the concepts of positive, negative and mixed-type solutions. Then, by using a fixed point theorem in cones, we obtain some existence and multiplicity results of such solutions. Furthermore, we also present some examples to illustrate our main results.