Department of Mathematics, Chungnam National University, Daejeon 305-764, South Korea
Copyright © 2010 Eunyoung Son et al. This is an open access article distributed under the
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Cădariu and Radu applied the fixed point theorem to prove the stability theorem of Cauchy and Jensen functional equations. In this paper, we prove the generalized Hyers-Ulam stability via the fixed point method and investigate new theorems via direct method concerning the stability of a general quadratic functional equation.