Geometry: Circles and Circumference Formula
Circles A circle is the set of all points in a plane that are the same distance from a given point, called the center.
Circles The circumference (C) is the distance around a circle. The diameter (d) is the distance across a circle through the center of the circle. The radius (r) is the distance from the center to any point on the circle.
Circles Pi is a non-terminating and non-repeating number represented by the Greek letter (pi) 3.14 is often used as an approximation for .
Circles Formulas for finding Circumference C = d C = 2r If you are given the diameter in a problem use the formula with d. If you are given a problem with the radius use the formula with r. Both formulas find the circumference.
Find Circumference Which formula for C will you use? C = 2r C = 131.9 inches 21 in
Your Turn Find the Circumference Which formula for C will you use? C = d C = (4.5) C = 14.1cm 4.5cm
Circles - Area Formula for finding the area of a circle: A = r If you are given the diameter instead of the radius; divide the diameter by 2 to get the radius. 2
Find the Area D = 14 m r = ? 14 ÷ 2 = 7 m A =r A =(7 ) A = (49) A = 153.9 m 14m 2 2 2
Your Turn Find the Area A =r A =(5 ) A = (25) A = 78.5 ft 2 2 5 ft