# Circle Theorems Revision

## 01 – Circle basics

Basic Circle Theorem Rules:

The ‘radius’ of a circle is the distance from the centre to its edge.

The ‘diameter’ of a circle is the distance between one edge of a circle, through its centre, to the edge on the other side.

The diameter of a circle is twice the value of its radius.

The ‘circumference’ is the distance around the edge of a circle. The circumference of a circle can be calculated by the formula: 2πr or πD

The ‘area’ of a circle can be calculated by the formula: πr²

The ‘tangent’ to a circle is a line which touches a circle at one point; without cutting across the circle.

An ‘arc’ is part of the circumference of a circle.

A ‘chord’ a line which goes from one point to another on the circle’s circumference.

A ‘sector’ is a pie-slice portion of a circle, e.g. a semicircle because it is a half of the whole circle.

A ‘segment’ is the portion of a circle between a chord of a circle and its associated arc.

The angle x is an angle ‘subtended’ by the arc.

A circle of diameter 10cm has an arc length π cm.

How many arcs are in a circumference?