# Periodic solutions for $n$-th order delay differential equations with damping terms

## Lijun Pan

Address: School of Mathematics, Jia Ying University, Meizhou Guangdong, 514015, P. R. China

E-mail: plj1977@126.com

Abstract: By using the coincidence degree theory of Mawhin, we study the existence of periodic solutions for $n$ th order delay differential equations with damping terms $x^{(n)}(t)=\sum \limits ^{s}_{i=1}b_{i}[x^{(i)}(t)]^{2k-1}+ f(x(t-\tau (t)))+p(t)$. Some new results on the existence of periodic solutions of the investigated equation are obtained.

AMSclassification: primary 34C25.

Keywords: delay differential equations, periodic solution, coincidence degree.