Solving the Functional Equation f(x - y) = f(x) - f(y)

Picked one by one from a mixed channel; title passed two strict editor passes and the clickbait rules.

A 6-minute video from SyberMath: “Solving the Functional Equation f(x - y) = f(x) - f(y)”.

Video by SyberMath, played through YouTube's embedded player.