BOUBOSSELA, WassilaBIROUD, Kheir eddine2024-12-152024-12-152020http://dspace.univ-temouchent.edu.dz/handle/123456789/5938In this memory,we focus on the existence of solution for a nonlinear boundary problem of third and fourth differential equations using the method of upper and lower solutions and some fixed point theorems like Larey Schauder theorem and Guo-Krasnosel’skii and expansion of cones. .frEquations différentielles ordinaires ,Problèmes aux limites, Sous et sur solutions, Solutions positives, Points fixes,Cône.Ordinary differential equaion, Boundary value problems,Lower and upper solutions, Positive solution, Fixed point, Cone.Thesis