The LessonAn 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 AngleAngles 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 AngleAn 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 AnglesThe 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°|
Interactive Game on the Types of Angles
- Click on an angle so it drops into the correct "bucket."
- In total, there are 10 angle to clear.
- If an angle drops into the wrong "bucket," you will lose one of your three lives.
- Good luck!
Parts of an AngleAn 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.