فهرست نشریات علمی دسترسی آزاد ایران

There has been extensive work on the existence of periodic solutions for nonlinear second order autonomous differantial equations, but little work regarding the third order problems. The popular Poincare-Bendixon theorem applies well to the former but not the latter (see [2] and [3]). We give a necessary condition for the existence of periodic solutions for the third order autonomous systems, This may become useful in further investigations. Our claims are proved and supported by certain examples.