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Approximately quadratic mappings on restricted domains. (English) Zbl 1215.39036
The authors investigate the functional equation f(rx+sy)+rsf(x-y)=rf(x)+sf(y) where f is given between vector spaces and reals r,s are assumed to be positive with the property r+s=1. Some Hyers-Ulam stability results are also presented under restrictions on the variables.
MSC:
39B82Stability, separation, extension, and related topics
39B22Functional equations for real functions
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