Exact multiplicity for periodic solutions of Duffing type Original Research Article

In this paper, we study the following Duffing-type equation: x″+cx′+g(t,x)=h(t), where g(t,x) is a 2π-periodic continuous function in t and concave–convex in x, and h(t) is a small continuous 2π-periodic function. The exact multiplicity and stability of periodic solutions are obtained.