If you are familiar with circles, solving Arc problems is relatively easy. An arc is a part of a circle’s circumference. The following figure shows an example of an arc.
The length of the arc can be determined if you know the angle the arc subscribes at the center (angle 
shown in the above figure). In other words, it is the angle at the center between the radii that make up the arc.
shown in the above figure). In other words, it is the angle at the center between the radii that make up the arc.
The length of the arc can be calculated using the following formula:
In the above formula, is the angle subscribed at the center in degrees.
is the angle subscribed at the center in degrees.
If you cannot remember that formula, do not worry. You can easily derive it if you understand the basic concept:
The length of the arc is directly proportional to the angle subscribed at the center. By now you know that the angle subscribed by the circle at the center is 360°. In effect the circumference of the circle is one giant arc with angle 360° at the center. You also know that circumference of the circle is 
.
.
Circumference with angle 360° subscribed at the center 
Arc with angle ° subscribed at the center
° subscribed at the center 
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