won{gil park [won{gil park, j. math. anal. appl., 376 (1) (2011) 193{202] proved the hyers{ulam stability of the cauchy functional equation, the jensen functional equation and the quadraticfunctional equation in 2{banach spaces. one can easily see that all results of this paper are incorrect.hence the control functions in all theorems of this paper are not correct. in this paper, we correctthes...

The stability problem of functional equations was originated from a question of Ulam 1 concerning the stability of group homomorphisms. Let G1 be a group and let G2 be a metric group with the metric d ·, · . Given > 0, does there exist a δ > 0 such that, if a function h : G1 → G2 satisfies the inequality d h xy , h x h y < δ for all x, y ∈ G1, then there exists a homomorphism H : G1 → G2 with d...