Resumen de Superstability of approximate cosine type functions on the monoid R2
Belaid Bouikhalene, Elhoucien Elqorachi, A. Charifi
In this paper, we study the superstability problem for the cosine type functional equation f(x1x2; x1y2 + x2y1) + f(x1x2; y1x2 .. x1y2) = 2f(x1; y1)f(x2; y2) on the commutative monoid (R2, X). As a result we obtain cosine type functions satisfying the equation approximately.
