If is a polynomial function satisfying and if

MATHEMATICS · Subjective · AoPS · Mathematics · Functions · Functions

Problem

If ff is a polynomial function satisfying 2+f(x)⋅f(y)=f(x)+f(y)+f(xy),∀x,y∈R2 + f(x) \cdot f(y) = f(x) + f(y) + f(xy), \forall x, y \in R and if f(2)=5f(2) = 5 , find f(f(2))f(f(2)) .

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