Friday, 13 July 2018

functional equations - If a function is like f(f(y))=a2+y, does it imply that f is surjective?

If a function is like f(f(y))=a2+y, does it imply that f is surjective?




Just for an example, consider this:




Find all functions f:RR such that f(xf(x)+f(y))=(f(x))2+y

for all real values of x,y.
It's solution begins as follows:
Let f(0)=a. Setting x=0 we get f(f(y))=a2+y yR




Now we can say that the range of a2+y is all real numbers, so f is surjective.




What if f(a,b) where (a,b) is some smaller interval?

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