RIAZI, NisrinBelattar, Zoukha2024-12-112024-12-112023http://dspace.univ-temouchent.edu.dz/handle/123456789/5887In this memoir, we study the solution of perturbed differential equations We will then examine the Poincaré perturbation method and apply this method to: algebraic differential equations, differential equations with an initial condition and boundary problems. Finally, we study the Lindstedt-Poincaré method applied to nonlinear differential equations to analyze the existence of periodic solutions.frThesis