## The Lesson

There are different types of angle. Angles can be:### Acute Angles

An acute angle is an angle of less than 90°.### Right Angles

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".