ISSN : 1226-0657
In this paper, we investigate the generalized Hyers-Ulam stability of a bi-Jensen functional equation <TEX>$4f(\frac{x\;+\;y}{2},\;\frac{z\;+\;w}{2})$</TEX> = f(x, z) + f(x, w) + f(y, z) + f(y, w). Also, we establish improved results for the stability of a bi-Jensen equation on the punctured domain.
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