A circle has 360 degrees of arc. In the circle shown, O is the center of the circle and angle AOC is a central angle of the circle. From the figure, the two diameters that meet to form angle AOC are perpendicular, so the measure of angle AOC is
90°. This central angle intercepts minor arc AC, meaning minor arc AC has
90° of arc. Since the circumference (length) of the entire circle is 36, the length of minor arc AC is
×36=9Choices B, C, and D are incorrect. The perpendicular diameters divide the circumference of the circle into four equal arcs; therefore, minor arc AC is
of the circumference. However, the lengths in choices B and C are, respectively,
and
the circumference of the circle, and the length in choice D is the length of the entire circumference. None of these lengths is
the circumference.