Question 21
Find all real-valued functions $f$ defined on the set of real numbers such that
$$
f(f(x) + y) + f(x + f(y)) = 2f(xf(y))
$$
for any real numbers $x$ and $y$.
$$
f(f(x) + y) + f(x + f(y)) = 2f(xf(y))
$$
for any real numbers $x$ and $y$.
MathNet 2020 — Math Olympiad Vault — Part 04 Question 21
Math Olympiad Vault · MathNet 2020 — Math Olympiad Vault — Part 04