Stability of a quadratic type functional equation. (English) Zbl 1179.39036
Summary: We investigate some results concerning the stability of the following quadratic type functional equation:
\[ f(x+y)+f(x-y)+f(y+z)+f(y-z)+f(z+x)+f(z-x)=4f(x)+4f(y)+4f(z). \]
\[ f(x+y)+f(x-y)+f(y+z)+f(y-z)+f(z+x)+f(z-x)=4f(x)+4f(y)+4f(z). \]
MSC:
| 39B82 | Stability, separation, extension, and related topics for functional equations |
| 39B52 | Functional equations for functions with more general domains and/or ranges |
