... vol. 6, no. 1, pp. 1 10 , 20 09. 22 J. Brzde¸k, “On stability of a family of functional equations,” Acta Mathematica Hungarica, vol. 12 8, no. 1- 2, pp. 13 9 14 9, 2 010 . 23 J. Brzde¸k and J. Sikorska, ... Qfy≤ 2 .11 for all x, y > 0,withxkys≥ d. Then one hasfx− f 1 ≤ 4 2 . 12 for all x ∈ R.Proof. We prove 2 . 12 only for the case that p/ P and p or P is ... USA, 19 98. 11 S M. Jung, “Hyers-Ulam-Rassias stability of Jensen’s equation and its application,” Proceedings of theAmerican Mathematical Society, vol. 12 6, no. 11 , pp. 313 7– 314 3, 19 98. 12 ...