In this paper we prove the Hyers-Ulam-Rassias stability by considering the cases that the approximate remainder ${varphi}$ is defined by $f(x{ast}y)+f(x{ast}y^{-1})-2g(x)-2g(y)={varphi}(x,y)$, $f(x{ast}y)+g(x{ast}y^{-1})-2h(x)-2k(y)={varphi}(x,y)$, where (G, *) is a group, X is a real or complex Hausdorff topological vector space and f, g, h, k are functions from G into X.