Question 99
Find all functions $f: \mathbb{R} \rightarrow \mathbb{R}$ which satisfy
$$
f(x+y)=f(x-y)+4 x y
$$
for all real numbers $x$ and $y$.
$$
f(x+y)=f(x-y)+4 x y
$$
for all real numbers $x$ and $y$.
MathNet 2026 — Part 10 Question 99
Math Olympiad Vault · MathNet 2026 — Part 10