angle

An angle is the size of the rotation between two straight lines that meet at a specific point. This is the angle’s vertex.

There are several types of angles:

• acute angle

• right angle

• obtuse angle

• reflex angle.

We can measure angles in different ways:

• by using a fraction, for example, half turn or quarter turn

• by using degrees (°) where a complete turn is 360°

• by using radians (rad) where a complete turn is 2π rad.

We use a protractor to draw and measure angles. However, some angles, for example 30°, 45°, 60°, 90°, can be drawn using only a ruler and compass.

A vertex in a polygon has two angles:

• interior angle

• exterior angle.

Together, the interior angle and the exterior angle will add up to a total of 360°.

Some angles can be discovered without being measured. For example, vertically opposite angles, alternate angles or corresponding angles.