1. Whiteboardmaths.com
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2. 4 Sectors
The Area of a Circle
Transform

3. 8 Sectors
The Area of a Circle
Transform

4. 16 Sectors
The Area of a Circle
Transform

5. A = πr x r = πr2 πr ½C ? r 32 Sectors
As the number of sectors  , the transformed shape becomes more and more like a rectangle. What will the dimensions eventually become?
32 Sectors
Remember
C = 2πr
Transform πr ½C r
A = πr x r = πr2

6. The Area of a Circle A = r2 1 2
Find the area of the following circles. 1 2
8 cm
9.5 cm
A = r2
A =  x 82
A = cm2 (1 dp)
A = r2
A =  x 9.52
A = cm2 (1 dp)

7. The Area of a Circle A = r2 3 4
Find the area of the following circles.
6 mm 3
2.4 m 4
A = r2
A =  x 32
A = 28.3 mm2 (1 dp)
A = r2
A =  x 1.22
A = 4.5 m2 (1 dp)

8. A = r2 Find the area of the clock face and radar screen. 12 cm 60 cm
A =  x 122
A = cm2 (1 dp)
A = r2
A =  x 302
A = 2827 cm2 (nearest cm2)

9. The Area of a Circle A = r2 1 2
Find the area of the following semi-circles. 1 2
8 cm
9.5 cm
A = ½r2
= ½ x  x 42
= 25.1 cm2 (1 dp)
A = ½r2
= ½ x  x 4.752
= 35.4 cm2 (1 dp)

10. The Area of a Circle A = r2 3 4 Find the area of the ¼ and ¾ circles.
6 cm
8.5 cm
A = r2
A = ¼r2
= ¼ x  x 62
= 28.3 cm2 (1 dp)
A = ¾r2
= ¾ x  x 8.52
= cm2 (1 dp)

11. The Area of a Circle A = r2 6 5
Find the radius/diameter of the following circles.
A = 25 cm2 find the diameter. 6 5
A = 30 cm2 find the radius.
r2 = 25
r2 = 25/
r = (25/)
r = 2.82
d = 2 x 2.82 = 5.6 cm 1dp
r2 = 30
r2 = 30/
r = (30/)
r = 3.1 cm 1dp