Britannica
Sources used in this answer
How are triangles classified by angle measurements?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
geometry
This map spans a millennium of prominent Greco-Roman mathematicians, from Thales of Miletus (c. 600 bce) to Hypatia of Alexandria (c. 400 ce).
In geometry, triangles are classified based on their interior angle measurements into three primary categories:1
- Acute triangles: These triangles possess three acute angles, meaning all interior angles are less than 90 degrees.21
- Obtuse triangles: These triangles contain a single obtuse angle, which is an angle greater than 90 degrees.31
- Right triangles: These triangles feature exactly one right angle (a 90-degree angle).41
In Euclidean geometry, the sum of these three interior angles must always equal 180 degrees.1