Stability of 2-variable additive-quadratic-cubic-quartic functional equation using fixed point method

In this paper, the authors proved the generalized Ulam-Hyers stability of 2-variable Additive-QuadraticCubic-Quartic functional equation$$\begin{aligned}f(x+2 y, u+2 v)+f(x-2 y, u-2 v)= & 4 f(x+y, u+v)-4 f(x-y, u-v)-6 f(x, u)+f(2 y, 2 v) \\& +f(-2 y,-2 v)-4 f(y, v)-4 f(-y,-v)\end{aligned}$$using fixed point method.