The area of an Arbelos

The figure below is an Arbelos, which means shoemaker's knife in Greek. Segment BD is constructed perpendicular to diameter AC at B. A circle is constructed with BD as the diameter. 1. Drag the BLUE points in the figure below. Which property of an Arbelos is suggested by the sketch? 2. Using similar triangles, PROVE the property you observed from part 1. Hint: Begin by finding the area of the Arbelos when AC = 1 unit.