1. Circumference & Area of Circles Unit 5-3

2. Circumference Formula for Circumference: ** r is the radius ** ** 2r = d. d is the diameter. ** **Circumference is the perimeter of the circle. **

3. Circumference 6 cm Always write out the formula to start with C = 2 π r Check if you have radius or diameter r = 6 Substitute into the formula C = 2 π (6) C = 12 π or C = 37.70 Don’t forget units! cm

4. Circumference 7.6 cm C = 2 π r d = 7.6 C = 2 π (3.8) C = 7.6 π or C = 23.88cm r = 3.8

5. YOUR TURN -Calculate the perimeter of these circles. 4 cm 8.2 in 7 ft 11 cm 25.13 cm 25.76 in 34.56 cm 43.98 ft

6. Circumference Given the Circumference, find the radius and diameter. C = 25 ft

7. YOUR TURN Given the Circumference, find the radius and diameter.

8. Area Formula for Area: ** r is the radius **

9. Area 6 cm Always write out the formula to start with A = π r 2 Check if you have radius or diameter r = 6 Substitute into the formula A = π (6) 2 A = 36 π or A =113.10 Don’t forget units! cm 2

10. Area 7.6 cm A = π r 2 d = 7.6 A = π (3.8) 2 A = 14.44 π or A = 45.36cm 2 r = 3.8

11. YOUR TURN -Calculate the area of these circles. 4 cm 8.2 in 7 ft 11 cm 50.27 cm 2 52.81 in 2 95.03 cm 2 153.94 ft 2

12. Area Given the Area, find the radius and diameter. A = 75 ft 2

13. YOUR TURN Given the Area, find the radius and diameter.