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The Circumference of a Circle diameter(d) Circumference (C) How many times does the diameter fit around the circumference? Choose your number. 11½22½33½4  = d radius In terms of the radius: C =? C =2  r

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

Find the circumference of the following circles. C =  d C = 2  r 8 cm cm 2 C =  d C=  x 8 C = 25.1 cm (1 dp) C =  d C=  x 9.5 C = 29.8 cm (1 dp)

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) The Circumference of a Circle Find the circumference of the following circles. C =  d C = 2  r 3 mm m 3

23 cm 7.5 cm Find the circumference of the tyre and steering wheel. C =  d C=  x 23 C = 72.3 cm (1 dp) C = 2  r C = 2 x  x 7.5 C = 47.1 cm (1 dp)

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

Perimeter = ¼ ( 2  r) + 2r = ¼ x 2 x  x x 6 = 21.4 cm (1 dp) Perimeter = ¾(2  r) + 2r = ¾ x 2 x  x x 8.5 = 57.1 cm (1 dp) The Circumference of a Circle Find the perimeter of the ¼ and ¾ circles. C =  d C = 2  r cm 8.5 cm

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