Compléter Circle FactsVersion en ligne Math Notes 8.3.2 par Sister Karol Joseph 1 similar Circumference perimeter another is circle Since The area of a with radius r = 1 unit is ? units^2 . ( Remember that ? ? 3 . 1415926 . . . ) Since all circles are , their areas increase by a square of the linear scale ( zoom ) factor . That is , a circle with radius 6 has an area that is 36 times the area of a circle with radius 1 . Thus , a circle with radius 6 has an area of 36 ? units^2 , and a circle with radius r has area A = ? r^2 units^2 . Area = ? r^2 = 2 ? r = ? d The circumference of a circle is its . It is the distance around a circle . The circumference of a circle with radius r = 1 unit is 2 ? units . Since the perimeter ratio is equal to the ratio of similarity , a circle with radius r has circumference C = 2 ? r units . Since the diameter of a circle is twice its radius , way to calculate the circumference is C = ? d units . A part of a circle is called an arc . This a set of points a fixed distance from a center and is defined by a central angle . a circle does not include its interior region , an arc is like the edge of a crust of a slice of pizza . A region that resembles a slice of pizza is called a sector . It is formed by two radii of a central angle and the arc between their endpoints on the circle .