“…Further generalizations on the above stability results was given in [16,21,22,40]. Since then several stability problems for various functional equations have been investigated in [1, 3-13, 17, 25, 34, 37, 39, 47]; various fuzzy stability results concerning Cauchy, Jensen, quadratic and cubic functional equations were discussed in [19,20,[29][30][31][32][43][44][45]. Jun and Kim [26] considered the following functional equation It is easy to show that the function f (x) = x 4 satisfies the functional equation (1.2), which is called a quartic functional equation and every solution of the quartic functional equation is said to be a quartic function.…”