ZEDIRI, Sounia2022-05-312022-05-312022http//localhost:8080/jspui/handle/123456789/4293This thesis contain a results of the existence of positive solutions of certain nonlinear elliptic and parabolic systems, involving the (p; q)-Laplace and the p(x)-Laplace operators. The method used to obtain the results is that of sub and supersolution, which is based on the maximum principle and the comparison theorem.enSub and supersolutions ; semipositon elliptic systems ; p(x)-Kircho¤ parabolic sys- temsThesis