Circles Learn to find the area and circumference of circles.

A circle is the set of points in a plane that are a fixed distance from a given point, called the center. A radius connects the center to any point on the circle. A diameter connects two points on the circle and passes through the center.

Radius Center Diameter Circumference The diameter d is twice the radius r. d = 2r The circumference of a circle is the distance around the circle.

A. Circle with a radius of 4 m C = 2r = 2(4) = 8m B. Circle with a diameter of 3.3 ft C = d = (3.3) = 3.3ft Find the circumference of each circle in terms of . 4m 3.3ft

A = r 2 = (4 2 ) = 16in 2 A. Circle with a radius of 4 in. Find the area of each circle in terms of  B. Circle with a diameter of 3.3 m A = r 2 = ( ) =  m 2 d2d2 = in 3.3m

Tweedle Dum & Tweedle Dee will help you remember your circle formulas! Tweedle Dum and Tweedle Dee Around the circle is pi times d. And if the area is declared Then its pi r squared.

A = r 2 = (3 2 ) = 9units 2 C = d = (6) = 6units Graph the circle with center (–2, 1) that passes through (1, 1). Find the area and circumference, in terms of 

C = d = (56)  176 ft  (56)  A Ferris wheel has a diameter of 56 feet and makes 15 revolutions per ride. How far would someone travel during a ride? Use for . Find the circumference The distance is the circumference of the wheel times the number of revolutions, or about 176  15 = 2640 ft.

Lesson Quiz Find the circumference of each circle in terms of  1. radius 5.6 m 2. diameter 113 m 11.2m 113mm Find the area of each circle in terms of . 3. radius 3 in. 4. diameter 1 ft 9in ft 2