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The Circle

The Circle. Special words Finding the circumference Finding the area. The distance from the centre of a circle to the edge is called the Radius. The distance from one edge of a circle to another (passing through the centre) is called the Diameter.

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The Circle

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  1. The Circle Special words Finding the circumference Finding the area

  2. The distance from the centre of a circle to the edge is called the Radius The distance from one edge of a circle to another (passing through the centre) is called the Diameter The distance all the way around the circle (its perimeter) is called the Circumference Special Words

  3. Objective Be able to find the circumference of a circle. Be able to find the perimeter of shapes with circular parts.

  4. Finding the circumference The formula for the circumference is Sometimes we are given the diameter C = πd 8cm C = 3.14 x 8 = 25.12 cm π = 3.14 (2dp)

  5. Finding the circumference C = πd C = 3.14 x 14 = 43.96 cm 14cm π = 3.14 (2dp)

  6. Finding the circumference Sometimes we are given the radius, r Now the formula for the circumference is C = 2πr But this is just half of the diameter, so we use 2r instead of d 5cm C = 2 x 3.14 x 5 = 31.4 cm π = 3.14 (2dp)

  7. Finding the circumference C = 2πr C = 2 x 3.14 x 3 = 20.09 m 3m π = 3.14 (2dp)

  8. What is the perimeter? 3m 12m The perimeter is the distance around the outside of the shape

  9. 3m 12m What is the shape made of?

  10. What is the shape made of?

  11. So really we have two shapes: A rectangle and a circle So this part gives us 12m + 12m = 24m 12m C = 2πr For this part, we find the circumference 3m C = 2 x 3.14 x 3 So the total perimeter is 24m + 18.84m = 42.84m = 18.84m

  12. Objective Be able to find the area of a circle. Be able to find the area of compound shapes with circular parts

  13. Finding the area Usually we are given the radius, r The formula for the area of a circle is A =πr2 A = 3.14 x 72 = 3.14 x 7 x 7 =153.86 cm2 7cm π = 3.14 (2dp)

  14. Finding the area If you are given the diameter, simply half this to find the radius first. The formula for the area of a circle is A =πr2 A = 3.14 x 42 = 3.14 x 4 x 4 = 50.24 m2 Here r = 4m 8m π = 3.14 (2dp)

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