• Journal of applied mathematics & informatics
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• v.9 no.1
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• pp.415-421
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• 2002

We extend the Hyers-Ulsam-Rassias stability of a quadratic functional equation f(χ+y+z)+f(χ-y)+f(y-Z)+f(χ-z) = 3f(χ)+3f(y)+3f(z) to Banach modules over a Banach algebra.