Generalized Hyers-Ulam Stability for a General Mixed Functional Equation in Quasi-β-normed Spaces

In this paper, we establish the general solution and investigate the generalized Hyers-Ulam stability of the following mixed additive and quadratic functional equation f(lambda x + y) + f(lambda x - y) = f(x + y) = f(x - y) + (lambda - 1)[lambda + 2)f (x) + lambda f(-x)], (lambda is an element of N, lambda not equal 1) in quasi-beta-normed spaces.