As in the preceding cases, the excess of the sum of the squares on AD and DB over the sum of the squares on AC and CB is also the excess of twice the rectangle AD by DB over twice the rectangle AC by CB, while twice the rectangle AD by DB exceeds twice the rectangle AC by CB by a rational area, for both are rational, therefore the sum of the squares on AD and DB also exceeds the sum of the squares on AC and CB by a rational area, which is impossible, for both are medial.