## 01 – Circle basics

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?**