On the approximate solution of Hosszus functional equation


1 Laboratory LIRST, Polydisciplinary Faculty, Departement of Mathematics, University Sultan Moulay Slimane, Beni-Mellal Morocco

2 National and Capodistrian University of Athens, Section of Mathematics and Informatics, 4, Agamemnonos Str., Aghia Paraskevi, Athens 15342, Greece

3 Faculty of sciences, Departement of Mathematics, University of Ibn Tofail, Kenitra, Morocco


We show that every approximate solution of the Hosszu's functional equation
$$f(x + y + xy) = f(x) + f(y) + f(xy) \ \text{for any}\ x, y\in \mathbb{R},$$
is an additive function and also we investigate the Hyers-Ulam stability of this equation in the following setting
$$|f(x + y + xy) - f(x) - f(y) - f(xy)|\leq\delta + \varphi(x; y)$$
for any $x, y\in \mathbb{R}$ and $\delta > 0$.