The Lesson
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. Angles can be measured in degrees (°) or in radians.
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:Angles can also be calculated using geometry and trigonometry.
Types of Angles
The different types of angles are:Type of Angle | Description | |
---|---|---|
Acute | Less than 90° | |
Right | 90° | |
Obtuse | Greater than 90° but less than 180° | |
Straight | 180° | |
Reflex | Greater than 180° | |
Full | 360° |
Interactive Game on the Types of Angles
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.