Kyungpook Mathematical Journal 2015; 55(1): 91-101
Published online March 23, 2015
Copyright © Kyungpook Mathematical Journal.
On the Stability of a Mixed Type Functional Equation
Yang-Hi Lee1 and Soon-Mo Jung2
1Department of Mathematics Education, Gongju National University of Education, Gongju, 314--711, Korea
2Mathematics Section, College of Science and Technology, Hongik University,
obreak{Sejong}, 339--701, Korea
In this paper, we investigate the stability of the functional equation
egin{align*}
&f(-x+y+z+w)+ f(x-y+z+w)+ f(x+y-z+w) + f(x+y+z-w) \
&~= 3f(x) + f(-x) + 3f(y) + f(-y) + 3f(z) + f(-z) + 3f(w) +
f(-w)
end{align*}
by using the direct method in the sense of Hyers.
Keywords: generalized Hyers-Ulam stability, Hyers-Ulam stability, direct method, mixed type functional equation