General Solution of a 2-variable Quadratic Functional Equation and Its Stability

One of the interesting questions in the theory of functional equations is the following: when is it true that a function which approximately satisfies a functional equation F must be close to an exact solution of F? If there exists an affirmative answer we say that the equation F is stable. In this paper, we obtain the general solution and the generalized Hyers- Ulam stability of the 2-variable quadratic functional equation which originating from quadratic form.