To derive the fact that the length of the arc of a circle intercepted by an angle is proportional to the radius of the circle, what should the arc length first be compared to?

To derive the fact that the length of the arc of a circle intercepted by an angle is proportional to the radius of the circle, the arc length should first be compared to the circumference of the circle. This is because the circumference of a circle is directly proportional to the radius, so by comparing the arc length to the circumference, we can establish the proportionality between the arc length and the radius of the circle.