By the end of this section you should be able to: ● understand the terms used to describe the parts of a circle ● understand what a sector of a circle is
Circles 1
Something to think about …
International Pi Day is celebrated on 14 March (3rd month, 14th day) around the world. Pi (Greek letter π ) is the symbol used in Mathematics to represent a constant — the ratio of the circumference of a circle to its diameter — which is approximately 3·14159.
On the right is a picture of a circular swimming pool surrounded by a circular concrete path. This path is then surrounded by a circular patch of grass.
Can you the fi nd the area covered by: (i) the pool, given that it has a 5 metre radius? (ii) the concrete path, given that it is 1 metre wide? (iii) the grass, given that it is 2 metres wide?
A circle is a two-dimensional shape made by drawing a curve that is always the same distance from a centre point. It has infi nite lines of symmetry.
The radius is the line segment joining the centre to a point on the circle. The plural of radius is radii.