Take the straight line with the chosen direction far from the region so that the region is completely on the same side with respect to it, for instance on the right side. We will build two graphs, representing the areas of the region that are located on the right and on the left of the line, as functions of the distance of the straight line from its initial position.
All’inizio tutta la regione è a destra della retta, il che significa che l’elemento sinistro dell’istogramma è nullo e quello destro rappresenta tutta l’area della regione.