Circle P6 2010 SA2 Nanyang P2 Q18

18. The figure below is created using the curved lines (arcs) of quadrants with radius 1 cm, 2 cm and 3 cm. Find the area of the shaded parts.
(Take pi as 3.14)

Circle of radius 3 cm  -  4 x Right-angled triangles of sides 3 cm -
[Circle of radius 1 cm  -  4 x  Right-angled triangles of sides 1 cm]
4 x Right-angled triangles  =  1/2  x  Diagonal  x  Diagonal

3.14 x 1 x 1 = 3.14

1/2 x 2 x 2 = 2

3.14 - 2 = 1.14

3.14 x 3 x 3 = 28.26

1/2 x 6 x 6 = 18

28.26 - 18 - 1.14 = 9.12 cm2

It was 9.12 cm2.