Classify Triangles

Key Concepts

• Classify triangles based on their sides and angles

Types of Triangles 

The triangles are classified based on sides and angles. 

Based on lengths of sides, the triangles are classified as follows: 

1. Equilateral triangle 
2. Isosceles triangle 
3. Scalene triangle   

Equilateral Triangle 

A triangle in which all its three sides are equal in length is called an equilateral triangle. 

Examples: 

Isosceles Triangle

A triangle in which two of its sides are equal is called an isosceles triangle. 

Examples: 

Scalene Triangle

A triangle in which all three sides are unequal in length is called a scalene triangle. 

Examples: 

Based on angles, the triangles are classified as follows: 

1. Acute triangle 
2. Obtuse triangle 
3. Right triangle  

Acute Triangle 

A triangle in which all the three angles are acute (i.e., less than 90°) is called an acute-angled triangle or acute triangle. 

Examples: 

Obtuse Triangle

A triangle in which one angle is obtuse (i.e., more than 90° but less than 180°) is called an obtuse-angled triangle or obtuse triangle. 

Examples: 

Right Triangle

A triangle in which any one of the angles is a right angle (i.e., 90°) is called a right-angled triangle or right triangle. 

Examples: 

Exercise

• Classify each triangle by its sides and by its angles.

Concept map

What have we learned

• Classfication of triangles based on sides.
• Classfication of triangles based on angles.