Tuesday, 7 May 2013

functions - Solution to functional equation and Cauchy

I want to show that the only continuos solutions to the functional equation
g(x)+g(y)=g(x2+y2)



is g(x)=cx2 where c is a constant i.e. c=g(1).



I think that I maybe could rewrite the equation, such that I could use the solution to Cauchy's functional equation i.e.



f(x+y)=f(x)+f(y)
with solutions cf(x), but i can't see how. Can anyone give med a hint?

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