1. AREA AND CIRCUMFERENCE OF A CIRCLE

2. diameter radius circumference The perimeter of a circle is called the circumference (C). The diameter (d) of a circle is twice the radius (r).

3. rearranging the sectors of the circle gives Consider dividing a circle into 8 equal sectors:

4. Now consider dividing the circle into 12 equal sectors: rearranging the sectors of the circle gives The more sectors there are, the closer the area gets to being a rectangle. r half circumference

5. Examples 1 Calculate a the circumference b the area of the circle. 8 cm a b

6. Examples 2 Calculate a the circumference b the area of the circle. 3.7 cm a b

7. Examples 3 The radius of the circle is 5 cm. The circle touches all four sides of the square. Calculate the shaded area. 10 cm

8. Examples 4 The radius of the large circle is 8 cm. The radius of the small circle is 5 cm. Calculate the shaded area.

9. Examples 5 The radius of the circle is 3 cm. The vertices of the square lie on the circumference of the circle. Calculate the shaded area. 6 cm x x Using Pythagoras

10. Examples 6 The area of the circle is 200cm 2. Find the value of r. r cm

11. Semicircles and quadrants A semicircle is half a circle.A quadrant is quarter of a circle.

12. Examples 1 Calculate a the perimeter b the area of the semicircle. 10 cm a b

13. Examples 2 Calculate a the perimeter b the area of the quadrant. 9 cm a b

14. Examples 3 The perimeter of the quadrant is 50 cm. Calculate the value of r. r cm

15. Examples 4 The diagram shows four identical circles of radius 4 cm. Calculate the shaded area.

16. Arcs and sectors An arc is part of the circumference of a circle. A sector of a circle is a region bounded by an arc and two radii. sector arc

17. O A B Examples 1 Finda the area of sector OAB b the length of arc AB c the perimeter of sector OAB. a b c

18. Examples 2 Finda the area b the perimeter of the shape. 7 m 3 m a b 126°