A Fixed Point Approach to the Stability of Quintic and Sextic Functional Equations in Quasi-β-Normed Spaces.

We achieve the general solution of the quintic functional equation f(x + 3y) - 5f(x + 2y) + 10f(x + y) - 10f(x) + 5f(x - y) - f(x - 2y) = 120f(y) and the sextic functional equation f(x + 3y) - 6f(x + 2y) + 15f(x + y) - 20f(x) + 15f(x - y) - 6f(x - 2y) + f(x - 3y) = 720f(y). Moreover, we prove the stability of the quintic and sextic functional equations in quasi-β-normed spaces via fixed point method. [ABSTRACT FROM AUTHOR]