Abstract
In this paper, using the direct and fixed point methods, we investigate the generalized Hyers-Ulam stability of the quintic functional equation:
2f(2x + y) + 2f(2x - y) + f(x + 2y) + f(x - 2y) = 20[f(x + y) + f(x - y)] + 90f(x)
in random normed spaces under the minimum t-norm.