“…This stability problem was first raised by Ulam [36] and thereafter it was further generalized in the works of Hyers [5] and Rassias [39]. It is a general concept which is applicable in diverse frameworks of mathematics like those in problems of differential equations [25,32,37], fixed points [20], isometrics [42], etc. Particularly for the functional equations, the Hyers-Ulam-Rassias stability has been considered in a good number of papers in different types of spaces [2, 3, 7, 10, 15, 21, 26, 27, 30, 33-35, 38, 43-45].…”