Difficulty: Medium In the figure above, inscribed triangle ABC is equilateral. If the radius of the circle is r, then the length of arc AXB is a) b) c) d) e) HINT In a circle, if two chords have the same length, then their arcs must have the same length.

A: Explanation: An equilateral triangle has three equal sides, so the lengths of the three arcs must be equal, and thus each arc is   of the circumference of the circle. The circumference of the circle is 2  r, so the length of arc AXB is   of 2  r, or    .