On the stability of a quadratic Jensen type functional equation

In this paper we obtain the general solution of the quadratic Jensen type functional equation 9f x + y + z 3 + f (x) + f (y) + f (z) = 4 f x + y 2 + f y + z 2 + f z + x 2 and prove the stability of this equation in the spirit of Hyers, Ulam, Rassias, and G˘avruta.  2002 Elsevier Science (USA). All rights reserved