Hyers–Ulam Stability of the Quadratic Functional Equation

On the Generalized Stabilities of Functional Equations via Isometries

“…These researchers investigated various functional equations, including Jensen's and Pexider's equations, and established conditions under which hyperstability can be achieved. For some further results, related to the issue of hyperstability, we refer the reader to see ( [40], Thorem 8.3) (for a generalization of the quadratic equation), ( [41], Thorem 21.3) (for the equations of homomorphism for square symmetric groupoids, considered in a class of set-valued mappings), ([42], Thorem 1) (for a functional equation in one variable in a class of set-valued mappings) and [43] (for functional equations of trigonometric forms in hypergroups).…”

Generalized Hyers-Ulam Stability of Trigonometric Functional Equations

“…Since that period, the corresponding area has become a very vibrant domain of research and stability problems for several functional equations have been extensively investigated by a number of authors (cf. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]).…”

On functional inequalities associated with Drygas functional equation

“…In [7], E. Elqorachi et al proved that if the function f : G → E from G (an abelian 2-divisible group) to an inner product space E, satisfies the inequality…”