RABIA, Afef Amina2024-03-242024-03-242022https://dspace.univ-annaba.dz//handle/123456789/3392The objective of this thesis is to provide sufficient conditions for the existence of periodic solutions for various differential systems perturbed by a small parameter using the averaging theory. We consider the problem of finding the limit cycles for some classes of Duffing differential equation and for two differential systems in R5 and R6 , using averaging theory of the first order.PDFenaveraging theory; differential system; duffing equation; liénard equation; limit cycle; periodic solutionThesis