Periodic solutions for a nonautonomous ordinary differential equation

We consider the nonautonomous differential equation of second order x″+a(t)x−b(t)x2+c(t)x3=0x″+a(t)x−b(t)x2+c(t)x3=0, where a(t),b(t),c(t)a(t),b(t),c(t) are TT-periodic functions. This is a biomathematical model of an aneurysm in the circle of Willis. We prove the existence of at least two positive TT-periodic solutions for this equation, using coincidence degree theories.