Suppose that triangle ABC has a 30-degree angle at A and a 60-degree angle at B. Let O be the midpoint of AB. Draw the circle centered at O that goes through A. Explain why this circle also goes through B and C. Angle BOC is called a central angle of the circle because its vertex is at the center. The minor arc BC is called a 60-degree arc because it subtends a 60-degree angle at the center. What is the angular size of minor arc AC? of major arc AC? How does the actual length of minor arc AC compare to the length of minor arc BC?