On the stability of the quadratic mapping in normed spaces
2001 ◽
Vol 25
(4)
◽
pp. 217-229
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Keyword(s):
The Hyers-Ulam stability, the Hyers-Ulam-Rassias stability, and also the stability in the spirit of Gavruţa for each of the following quadratic functional equationsf(x+y)+f(x−y)=2f(x)+2f(y),f(x+y+z)+f(x−y)+f(y−z)+f(z−x)=3f(x)+3f(y)+3f(z),f(x+y+z)+f(x)+f(y)+f(z)=f(x+y)+f(y+z)+f(z+x)are investigated.