Classifying triangles

In this lesson, we will learn:

• How to classify triangles by their side lengths
• How to classify triangles by their angles

• 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:
1. By their side lengths
2. 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