Hyers-Ulam-Rassias stability of a composite functional equation in various normed spaces

Abstract

In this paper, we prove the generalized Hyers-Ulam(or Hyers-Ulam-Rassias ) stability of the following composite functional equation <br /> <br />f(f(x)-f(y))=f(x+y)+f(x-y)-f(x)-f(y) <br /> <br /> in various normed spaces.