We all know that circles have a measure of 360°, right? The angle measure of the given sector is 72°, so it's
. Simplify this and it becomes 1/5 of 360 degrees. Now that we have the proportion, use the circumference formula of 2πr. I'll be using 3.14 for pi, which gives us a circumference of 22.8 units. Circumference is the length around a circle, but in this case, we only want the length around this part of the circle. This means we want to multiply 22.8 × 1/5, which becomes
This simplifies into 4.56 units.