## The Lesson

There are different types of angle. Angles can be:

### Acute Angles

An acute angle is an angle of less than 90°. A right angle is an angle of 90°. Don't forget: Right angles are often denoted by adding a small right angle that forms a square with the angle.

### Obtuse Angles

An obtuse angle is an angle greater than 90° and less than 180°. ### Straight Angles

A straight angle is an angle of 180°. ### Reflex Angles

A reflex angle is an angle greater then 180° and less than 360°. ### Full Angles

A full angle is an angle of 360°. ## Interactive Widgets

Try our bucket game or our drag-and-drop game to help you learn about the types of angles.

## What Is an Angle?

An angle is created by two rays that have a common end point, called the vertex. ## Who Classified Angles?

Euclid classified angles in his book, Elements. Definition 10: "When a straight line standing on a straight line makes the adjacent angles equal to one another, each of the equal angles is right". Definition 11: "An obtuse angle is an angle greater than a right angle". Definition 12: "An acute angle is an angle less than a right angle".

## Oblique Angles

Acute and obtuse angles are also oblique angles. Oblique angles are neither right angles nor multiples of right angles.