STABILITY PROBLEMS OF CUBIC MAPPINGS WITH THE FIXED POINT ALTERNATIVE
We investigate the general solution of the cubic functional equation 3f (2x + y) + f(2x - y) + 6f(y) = 8f(x + y) + 24f(x) on the real vector spaces and then we prove the generalized Hyers-Ulam-Rassias stability in quasi-beta-normed spaces, the stability by using a subadditive function and then the stability by using the alternative fixed point method.
cubic mapping fixed point functional equation hyers-ulam-rassias stability quasi-beta-normed space subadditive function