Stability of the second order partial differential equations

We say that a functional equation ( ξ ) is stable if any function g satisfying the functional equation ( ξ ) approximately is near to a true solution of ( ξ ). In this paper, by using Banach's contraction principle, we prove the stability of nonlinear partial differential equations of the following forms: y x ( x , t ) = f ( x , t , y ( x , t ) ) , a y x ( x , t ) + b y t ( x , t ) = f ( x , t , y ( x , t ) ) , p ( x , t ) y x t ( x , .