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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).  =. 1. 2. C =2 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)  = 1 2 C =2r 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 =d C =2r C =d C=  x 8 C = 25.1 cm (1 dp) C =d C=  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 =d 2.1 m C =2r C =2r C = 2 x  x 3 C = 18.8 mm(1 dp) C = 2r C = 2 x  x 2.1 C = 13.2 m(1 dp)

  5. Find the circumference of the tyre and steering wheel. 7.5 cm 23 cm C =2r C = 2 x  x 7.5 C = 47.1 cm(1 dp) C =d C=  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 =d C =2r Perimeter =½d + d = ½ x  x 9.5 + 9.5 = 24.4 cm (1 dp) Perimeter =½d + d = ½ x  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 =d C =2r Perimeter =¾(2r) + 2r = ¾ x 2 x  x 8.5 + 2 x 8.5 = 57.1 cm (1 dp) Perimeter =¼(2r) + 2r = ¼ x 2 x  x 6 + 2 x 6 = 21.4 cm (1 dp)

  8. C =d C =2r 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. 2r = 30 r = 30/(2) r = 4.8 cm (1 dp) d = 25 d = 25/ d = 8.0 cm (1 dp)

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