# Circumference & Area of Circles Unit 5-3. Circumference Formula for Circumference: ** r is the radius ** ** 2r = d. d is the diameter. ** **Circumference.

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Circumference & Area of Circles Unit 5-3

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

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

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

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

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

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

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

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

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

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