Types of angle

There are 360° in a full turn, 180° in a half turn and 90° in a quarter turn. A quarter turn is called a right angle.

360, 180 & 90 degree angles

A right angle is shown by a small square. This fact can be used to calculate unknown angles.


Calculate angle c.

90 degree angle, split into 20 degrees and unknown angle, c

A right angle is shown.

c = 90^\circ - 20^\circ = 70^\circ

There are three different types of angle.

Acute, obtuse and reflex angles

An acute angle is an angle less than 90°.

An obtuse angle is an angle between 90° and 180°.

A reflex angle is an angle between 180° and 360°.