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f ( x / (y + 1)) = 1 - xf(x + y)

Source: Switzerland - 2013 Swiss MO Final Round p4

December 30, 2022
algebrafunctionalfunctional equation

Problem Statement

Find all functions f:R>0R>0f : R_{>0} \to R_{>0} with the following property: f(xy+1)=1xf(x+y)f \left( \frac{x}{y + 1}\right) = 1 - xf(x + y) for all x>y>0x > y > 0 .