Periodic solutions for a kind of neutral Rayleigh equations with variable parameter (Q1936947)

A theorem on the existence of periodic solutions for a class of neutral Rayleigh equations with variable periodic parameter and delay argument \[ (x(t)- c(t)x(t-\tau))''+ f(x'(t))+ g(x(t-\gamma(t)))= e(t) \] is established by using the coincidence degree theory of Mawhin. The result obtained extend previous ones in the literature.