On the Superstability of Trigonometric Type Functional Equations
D. Zeglami *
Department of Mathematics, Faculty of Sciences, Ibn Tofail University, Kenitra, Morocco.
S. Kabbaj
Department of Mathematics, Faculty of Sciences, Ibn Tofail University, Kenitra, Morocco.
*Author to whom correspondence should be addressed.
Abstract
The aim of this paper is to study the superstability for the mixed trigonometric functional equation:
and the stability of the Pexider type functional equation:
where G is any group, not necessarily abelian f , g and h are unknown complex valued functions and σ is an involution of G. As a consequence we prove that if f satisfies the inequality 
for all x , y ∈ G then f is bounded.
Keywords: Superstability, d'Alembert's equation, Trigonometric functional equation, 2000 Mathematics Subject Classification, Primary 39B72.