Solvability of Periodic Boundary Value Problems for nth-Order Ordinary Differential Equations

In this paper, we prove existence results for periodic boundary value problems concerning the nth -order differential equationx(n)(t)=f(t,x(t),x′(t),…,x(n−1)(t)), t [0,1]. Our method is based upon the coincidence degree theory of Mawhin. The results obtained are new. Examples are given to illustrate the main results.