Question 168
Find the real functions $f$ of a real variable that satisfy the functional equation
$$
f(x+f(x+y))=f(2 x)+y
$$
for all real $x, y$.
$$
f(x+f(x+y))=f(2 x)+y
$$
for all real $x, y$.
MathNet 2018-part-05 — 181 problems (EN–VI) Question 168
Math Olympiad Vault · MathNet 2018-part-05 — 181 problems (EN–VI)