KöMaL 2025 B5459

Find all functions $f\colon\mathbb{Q}\rightarrow\mathbb{Q}$ satisfying $f(x)+f(y)=\frac{f(x+2y)+f(2x-y)}{5}$ for all rational numbers $x$ , $y$ .

Official text KöMaL. Quoted with source.

Solutions

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