Train tracks are made of metal. Consequently, they expand when it's warm and shrink when it's cold. When riding in a train, you hear the clickety-clack of the wheels going over small gaps left in the tracks to allow for this expansion. Suppose you were a beginner at laying railroad tracks and forgot to put in the gaps. Instead, you made a track 01 mile long that was firmly fixed at each end. On a hot day, suppose the track expanded by A = 8 feet and therefore buckled up in the middle, creating a triangle.