ORTHOGONAL STABILITY OF AN ADDITIVE-QUADRATIC FUNCTIONAL EQUATION IN NON-ARCHIMEDEAN SPACES

Abstract

Using the fixed point method, we prove the Hyers-Ulam stability of the orthogonally additive-quadratic functional equation 2f (x+y/2) + 2f (x-y/2) = 3/2 f(x) - 1/2 f(y) + 1/2f(-y) (0.1) for all x, y with x perpendicular to y, in non-Archimedean Banach spaces. Here perpendicular to is the orthogonality in the sense of Ratz.