Page 33 - Key Stage 3 Geometry

3 The Circle

There are four features you need

to know about at this stage in the

description of a circle.

1. The circumference which

is the visible rim of the circle (also
known as the perimeter).

2. The centre O which is equidistant from every

part of the circumference.
3. The diameter is a line that stretches from one

side of the circumference to the other and

passes through the centre. You will often come
across vertical diameter (which goes from north

point to the south point) and horizontal

diameter (which goes from east point to west
point).

4. The radius which stretches from the centre to
the circumference.

If the diameter is D, the length of the circumference is

πD, where π is 3.141592… a never ending number
referred to as a transcendental number. In the

following exercises you will be expected to use your

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