In this paper, we study the existence of the following optimum solution for the system of differential equation
(1) y’= Ay (t) + ¦(t, y (t)) t Î J = [0, T] y (t0)=y2,
(2) y’= Ay (t) + g (t, y (t)) t Î J = [0, T] y (t0)= y1
in a Hilbert spaces in which ¦, g: J×H®H are single-valued maps, {A (t)} tÎJ is a family of linear operators in H and y1 y2 Î H.We prove the existence of the pair (x, y) such that x , y are the solution of differential equation (1) and (2) and ||x-y||=||y1-y2||The pair (x, y) is called the optimum solution of the system of differential equation. Under suitable conditions on ¦, g and family of linear operators {A (t)}tÎJ. The results of the existence of the optimal solution are obtained by applying the best proximity points for the integral equation to the differential equation system.