Types of Angles
Acute <90°, right 90°, obtuse between 90° and 180°, straight 180°.
Key idea
Acute <90°, right 90°, obtuse between 90° and 180°, straight 180°.
In depth
Angles are named by size: acute is under 90°, right is exactly 90°, obtuse is between 90° and 180°, straight is 180°, reflex is between 180° and 360°. The names make it quick to describe and estimate shapes.
Worked example
37° is acute, 90° is right, 125° is obtuse, 200° is reflex.
Real-world uses
- Checking if a corner is square in carpentry
- Judging turns in navigation and sport
Common mistake
Calling 180° obtuse. A straight angle is its own category.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Types of Angles?
Acute <90°, right 90°, obtuse between 90° and 180°, straight 180°. It is a topic at the beginner level in Geometry.
Where is Types of Angles used in real life?
Real-world examples: Checking if a corner is square in carpentry; Judging turns in navigation and sport.
What should I learn before Types of Angles?
Make sure you are comfortable with Angles, the previous topic in Geometry.
What is a common mistake with Types of Angles?
Calling 180° obtuse. A straight angle is its own category.
How can I practise Types of Angles?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Types of Angles?
Move on to Measuring Angles with a Protractor next.
Related beginner topics in Geometry
- Points, Lines and Planes – The undefined building blocks of geometry.
- Line Segments and Rays – A segment has two endpoints; a ray starts at a point and goes on forever.
- Angles – Two rays sharing an endpoint; measured in degrees.
- Measuring Angles with a Protractor – Align the baseline and read the scale.
- Complementary and Supplementary – Pairs summing to 90° or 180°.
- Triangles: Classification – By sides (equilateral, isosceles, scalene) and by angles.