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Journal of Function Spaces and Applications
Volume 2013 (2013), Article ID 309098, 16 pages
Research Article

Stability of a Generalized Trigonometric-Quadratic Functional Equation

1School of Science, Walailak University, Nakhon Si Thammarat 80160, Thailand
2Department of Mathematics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand

Received 28 May 2013; Accepted 25 September 2013

Academic Editor: Jaeyoung Chung

Copyright © 2013 Janyarak Tongsomporn and Vichian Laohakosol. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A stability result for the generalized trigonometric-quadratic functional equation over the domain of a normed space and the range of a Banach space is derived. It states that under appropriate conditions on the function , the four functions , , , and are approximately equal to combinations of certain quadratic and additive functions.