Angles (Mathematics Glossary)
What Is an Angle?
An angle is created by two rays that have a common end point, called the vertex.
The angle is also a measure of the rotation between the two rays.
How to Identify an Angle
Angles are often identified using Greek letters (α, β, γ, θ, ψ). The letter theta θ is often used.
In geometric figures, points are often labelled with capital letters. Consider the angle made between points ABC, where the vertex is A and AB and AC are the rays:
The angle can be identified as the angle A, or by ∠BAC, where the middle of the 3 letters is the vertex.
How to Measure an Angle
An angle is measured by the shortest rotation between the two rays.
Angles are often measure in degrees, denoted °. There are 360 degrees in a full rotation.
Angles can also be measured in radians. There are 2π radians in a full rotation.
Angles can be measured directly using a protractor:
Types of Angles
The different types of angles are:
|Type of Angle||Description|
|Acute||Less than 90°|
|Obtuse||Greater than 90° but less than 180°|
|Reflex||Greater than 180°|
Parts of an Angle
An angle is created by two rays meeting at a common endpoint, the vertex.
A ray is a line which starts from a point.
A vertex is the point where the two rays meet.
What's in a Name?
Angle comes from the Latin word 'angulus' meaning "corner".
It has the same root as the word "ankle", because the foot forms a corner with the leg.