1. The problem statement, all variables and given/known data This is a question I had in a mathematics quiz I participated in today. The river bank of a river on the west coast is under observation perfectly. Suppose the temperature variation for the last one hundred years is known absolutely. The temperature now is exactly as it was 2007 years ago. Must there be at least one pair of years, separated by one year, which have the exact same temperature? 2. Relevant equations 3. The attempt at a solution I said yes as I thought the temperature change during a year would be a periodic function with period one (year). How could I prove or disprove it?