Length of an arc: An arc is a piece of the circumference. If n is the degree measure of the arc’s
central angle, then the formula is
In the figure above, the radius is 5, and the measure of the central angle is 72°. The arc length is
or of the circumference:
Area: The area of a circle is usually found using this formula in terms of the radius r :
Area of a Circle = πr^2The area of the circle above is π(4)^2 = 16π.
Area of a sector: A sector is a piece of the area of a circle. If n is the degree measure of the sector’s
central angle, then the area formula is