STABILITY OF A QUADRATIC FUNCTIONAL EQUATION IN VARIOUS NORMED SPACES

In this paper, we investigate the generalized Hyers-Ulam stability of the quadratic functional equation f(x + y + z) + f(x + (y)) + f(y + (z)) + f(x + (z)) = 3(f(x) + f(y) + f(z)) in various normed spaces by using the xed point method.