A functional equation from the IMO shortlist!

Equations are a lot harder when we start throwing functions into them! This problem comes from the 2018 shortlist for the International Math Olympiad. Check out more challenge problems here: https://www.youtube.com/playlist?list=PLug5ZIRrShJGkzGsXMYQt8bi5ImYtiEMM New math videos every Monday and Friday. Subscribe to make sure you see them!