Circles Circumference Area Circle is the set of

Circles: Circumference & Area Circle: is the set of all points in a plane that are equidistant from a given point, called the center of the circle. Radius: the distance from the center to a point on the circle. r Circumference: the distance around the circle (just like perimeter) Diameter: distance across the circle, through the center. Formulas: C = 2 r or C = d : Pi – the ratio of the circles circumference to its diameter 3. 14…

Circumference Formulas: C = 2 r or C = d is about 3. 14…use symbol in calculator Find the circumference of the following circles. Round your answer to the nearest tenth. EX 2 EX EX C = 2 r C = 2 • • 2 C = 4 12. 6 10 C = d C = • 10 C = 10 31. 4 The circumference of a circle is 10, What is its diameter in termsdiameter of ? = The radius of a circle is 8, What is the circumference in terms of ? C = 16

Area of a Circle Area = r 2 EX Find the area of the following circle. Round to the nearest tenth. 7 A= 72 A= 49 A = 153. 9 units 2 20 A = 314. 2 units squared EX The area of a circle is given as 95 square units. Find the diameter of the circle, to the nearest whole number. Diameter = 11 units EX The area of a circle is given as 25. Find the circumference in terms of . A = r 2 C = 2 r 25 = r 2 C = 2 • • r 25 = r 2 C = 10 5=r

More Examples: EX The circumference of a circle is 18. Find the area of the circle, leave answer in terms of . C=2 r A = r 2 18 = 2 r A = 92 9=r A = 81