Classifying triangles
Topic Notes
In this lesson, we will learn:
- How to classify triangles by their side lengths
- How to classify triangles by their angles
Notes:
- A triangle is a 2-dimensional (2D) shape with 3 straight sides and 3 angles
- A triangle’s angles always add up to 180° degrees
- Triangles can be classified in 2 ways:
- By their side lengths
- By the size of their angles
- When looking at side lengths, we classify triangles by how many sides are the same length (how many sides are “congruent”)
- If no sides are the same, it is a scalene triangle
- If two sides are the same, it is an isosceles triangle
- If all three sides are the same, it is an equilateral triangle
- When looking at the angles, we classify triangles by its biggest angle and comparing it with the right angle (are the angles smaller than, equal to, or greater than 90° degrees?)
- If all of the angles are smaller than 90° , it is an acute triangle
- If one of the angles is exactly 90° , it is a right triangle
- If one of the angles is bigger than 90° , it is an obtuse triangle
![Angles and Polygons: Classifying triangles](
https://dmn92m25mtw4z.cloudfront.net/img_set/math5-15-1-x-1/v1/math5-15-1-x-1-1323w.png)