2. Circles…… Area and Circumference

3. The Circumference of a Circle Find the circumference of the following circles. C =  d C = 2  r 8 cm 1 9.5 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)

4. 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 4 2.1 m 3

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

6. Perimeter = ¼ ( 2  r) + 2r = ¼ x 2 x  x 6 + 2 x 6 = 21.4 cm (1 dp) Perimeter = ¾(2  r) + 2r = ¾ x 2 x  x 8.5 + 2 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 3 4 6 cm 8.5 cm

7. A =  r 2 A =  x 8 2 A = 201.1 cm 2 (1 dp) A =  r 2 A =  x 9.5 2 A = 283.5 cm 2 (1 dp) The Area of a Circle Find the area of the following circles. A =  r 2 8 cm 1 9.5 cm 2

8. The Area of a Circle Find the area of the following circles. 6 mm 3 2.4 m 4 A =  r 2 A =  x 3 2 A = 28.3 mm 2 (1 dp) A =  r 2 A =  x 1.2 2 A = 4.5 m 2 (1 dp) A =  r 2

9. The Area of a Circle Find the area of the following semi-circles. 8 cm 1 9.5 cm 2 A = ½  r 2 = ½ x  x 4 2 = 25.1 cm 2 (1 dp) A = ½  r 2 = ½ x  x 4.75 2 = 35.4 cm 2 (1 dp) A =  r 2

10. A = ¼  r 2 = ¼ x  x 6 2 = 28.3 cm 2 (1 dp) A = ¾  r 2 = ¾ x  x 8.5 2 = 170.2 cm 2 (1 dp) The Area of a Circle Find the area of the ¼ and ¾ circles. 3 4 6 cm 8.5 cm A =  r 2

11.  r 2 = 25 r 2 = 25/  r =  (25/  ) r = 2.82 d = 2 x 2.82 = 5.6 cm 1dp A =  r 2 The Area of a Circle Find the radius/diameter of the following circles. A = 25 cm 2 find the diameter. 6 5 A = 30 cm 2 find the radius.  r 2 = 30 r 2 = 30/  r =  (30/  ) r = 3.1 cm 1dp

12. ARCS and SECTORS of CIRCLES Sector  O A B The angle  between two radii of a circle divides the circle into a minor and a major sector. The arc lengths of each sector are the minor and major arcs respectively. Arc

13. Example Question: The shape below is a sector of a circle of radius 8.4 cm. Find (a) the arc length and (b) sector area. 100 o 8.4 cm 160 o 3.1 m Now try this one.