IMO 2011 Shortlist A3
Determine all pairs (f,g) of functions from the set of real numbers to itself that satisfy g(f(x + y)) = f(x) + (2x + y)...
Category: Algebra
Problem
Determine all pairs (f,g) of functions from the set of real numbers to itself that satisfy g(f(x + y)) = f(x) + (2x + y)g(y) for all real numbers x and y.