Finding the length of an arc?

Question

If the radius of a circle is 15 meters represented by AC, which is connected to AB to make a 90 degree angle inside of a circle what is the length of the arc A to B to the nearest meter?
8.7 meters, 11.8 meters, 15.0 meters, or 23.9 meters

Answer 1

arc = angle/360 * 2pi*r

arc = 90/360 * 2pi*15

arc = 1/4 * 94.2

arc = 23.55 m

23.9 is closed to 23.55, so that's the answer

Answer 2

Since it's a right angle, you know it will be 1/4 of the perimeter, which is 2πr. So the answer is πr/2 = π(15)/2 = 23.6 m to the nearest 0.1 m.