Angles: Measuring Angles
Learn all about angles — what they are, how to measure them, and how to use them in math!
1. What is an Angle?
Definition: An angle is a figure formed by two rays that share a common starting point.
- The two rays are called the sides of the angle
- The common starting point is called the vertex
- The region between the sides is called the interior
Interactive visualization — available in the full lesson
2. Naming Angles
By Three Letters
∠ABC
The middle letter is always the vertex!
Read as "angle ABC"
By Vertex Only
∠B
Used when there's only one angle at that point
Read as "angle B"
By Number
∠1, ∠2
Used when angles are marked on a diagram
Read as "angle 1"