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The Circumference of a Circle

The Circumference of a Circle. How many times does the diameter fit around the circumference? Choose your number. 1. 1½ . 2 . 2½ . 3 . 3½ . 4 . d. diameter(d). In terms of the radius:. radius. C =? . Circumference (C). π =. 1. 2. C =2 π r. 3. The Circumference of a Circle.

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The Circumference of a Circle

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  1. The Circumference of a Circle How many times does the diameter fit around the circumference? Choose your number. 1 1½ 2 2½ 3 3½ 4 d diameter(d) In terms of the radius: radius C =? Circumference (C) π = 1 2 C =2πr 3

  2. The Circumference of a Circle It’s the same for all circles!

  3. The Circumference of a Circle Find the circumference of the following circles. 1 2 8 cm 9.5 cm C =πd C =2πr C =πd C= π x 8 C = 25.1 cm (1 dp) C =πd C= π x 9.5 C = 29.8 cm (1 dp)

  4. The Circumference of a Circle Find the circumference of the following circles. 4 3 3 mm C =πd 2.1 m C =2πr C =2πr C = 2 x π x 3 C = 18.8 mm(1 dp) C = 2πr C = 2 x π x 2.1 C = 13.2 m(1 dp)

  5. Find the circumference of the tire and steering wheel. 7.5 cm 23 cm C =2πr C = 2 x π x 7.5 C = 47.1 cm(1 dp) C =πd C= π x 23 C = 72.3 cm (1 dp)

  6. The Circumference of a Circle Find the perimeter of the following semi-circles. 1 2 8 cm 9.5 cm C =πd C =2πr Perimeter =½πd + d = ½ x π x 9.5 + 9.5 = 24.4 cm (1 dp) Perimeter =½πd + d = ½ x π x 8 + 8 = 20.6 cm (1 dp)

  7. The Circumference of a Circle Find the perimeter of the ¼ and ¾ circles. 3 4 8.5 cm 6 cm C =πd C =2πr Perimeter =¾(2πr) + 2r = ¾ x 2 x π x 8.5 + 2 x 8.5 = 57.1 cm (1 dp) Perimeter =¼(2πr) + 2r = ¼ x 2 x π x 6 + 2 x 6 = 21.4 cm (1 dp)

  8. C =πd C =2πr The Circumference of a Circle Find the diameter/radius of the following circles. 5 6 C = 25 cm find the diameter. C = 30 cm find the radius. 2πr = 30 r = 30/(2π) r = 4.8 cm (1 dp) πd = 25 d = 25/π d = 8.0 cm (1 dp)

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