Stability of cosine type functional equations onmodule extension Banach algebras

Let A be a Banach algebra and X be a Banach A-bimodule. In this paper we investigate the stability of the cosine type functional equation φ(ab,a·y+x·b)=φ(ab,x·b-a·y)=2φ(a,x)φ(b,y),on module extension Banach algebra U=A+X.

Keywords:

Stability , Cosine functional equations , multiplicative function