Let be an Abelian group, let be the field of complex numbers, and let . We consider the generalized Hyers-Ulam stability for a class of trigonometric functional inequalities, , where is an arbitrary nonnegative function.
"On a Generalized Hyers-Ulam Stability of Trigonometric Functional Equations." J. Appl. Math. 2012 1 - 14, 2012. https://doi.org/10.1155/2012/610714