Central AngleA central angle is an angle whose vertex is at the center of the circle.
2
The measure of a minor arc is the measure of its central angle.
The measure of a major arc is 360 minus the measure of its central angle.
The arc measure is written as
Central Angle
A
B
CBAC
Circumference Example:
2 (3)CExample: Find the circumference of the following circle.
3 cm6C
18.85C cm
• When finding the circumference of a circle, you can leave your answer in terms of pi.
Circumference:
Circumference is the distance around the circle.
2C r
2 (3)C
4
C d2d r
Formula: Or
Example: Find the circumference of the following circle.
3 cm6C
18.85C cm
where
Example: If a bicycle tire has a diameter of 26 inches, how far does it travel in 1000 revolutions of the tire? Use 3.14.
Example: The rim of a satellite dish has a diameter of 7 feet. Find the circumference of the rim and the area of the circle defined by the rim. Use 3.14.
Example: A Ferris wheel has diameter of 42 feet. How far will a rider travel during a 4 minute ride if the wheel rotates once every 20 seconds? Use 22/7.
Example: The tires of a racing bike are approximately 70 cm in diameter. How far does a bike racer travel in 5 minutes if the wheels are turning at a speed of 3 revolutions per second? How many revolutions does a wheel make in 22 km race? Use 22/7.
Area of a Circle
Area of a circle is the number of unit squares that can fit into a circle.
2(3)A 9A
7
2A r
Example: Find the area of the following circle.
3 cm
228.27A cm
Formula: