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:R↦R 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 ∀y∈R
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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