MathDB
f(x)+ f(y) = f(x+2xy)+ f(y-2xy), f(-1) = f(1)

Source: Czech And Slovak Mathematical Olympiad, Round III, Category A 1993 p5

February 20, 2020
functional equationfunctionalalgebra

Problem Statement

Find all functions f:ZZf : Z \to Z such that f(1)=f(1)f(-1) = f(1) and f(x)+f(y)=f(x+2xy)+f(y2xy)f(x)+ f(y) = f(x+2xy)+ f(y-2xy) for all x,yZx,y \in Z