Select point B, and drag it. As you drag B, circle AB changes. Verify that you can make circle AB coincide with AC. Return B to its approximate initial position. When circle AB coincides with circle AC, what do you notice about the regions CAD and EAF? In terms of similarity, what does your observation imply about the relationships among the lengths of the radii of AB and AC and the lengths of arc EF and arc CD? Write the relationship in the form of a proportion, and explain how it follows from your observation.