Lee, An and Park introduced the quadraticfunctional equation and proved the stability of the quadratic functional equation in the spirit of Hyers, Ulam and Th. M. Rassias. Using the fixed point method, we prove the generalized Hyers-Ulam stability of the quadraticfunctional equation in Banach spaces.
"The Stability of a Quadratic Functional Equation with the Fixed Point Alternative." Abstr. Appl. Anal. 2009 1 - 11, 2009. https://doi.org/10.1155/2009/907167