THE STABILITY OF PEXIDERIZED COSINE FUNCTIONAL EQUATIONS

In this paper, we investigate the superstability problem for the pexiderized cosine functional equations f(x+y)+f(x-y) = 2g(x)h(y), f(x + y) + g(x - y) = 2f(x)g(y), f(x + y) + g(x - y) = 2g(x)f(y). Consequently, we have generalized the results of stability for the cosine(d'Alembert) and the Wilson functional equations by J. Baker, P. G·avruta, R. Badora and R. Ger, and G.H. Kim.