For any arc of the radian measure(in radians), its length is , where "r" is the radius of the circle. So, convert 72 degrees to radians and use this formula. Alternatively, you may notice that 72 degrees is of the full angle of 360 degrees, so 72 degrees is of radians: 72 degrees = radians. THEREFORE, the arc length is = = 7.536 cm. ANSWER