Classification of triangles

From Karnataka Open Educational Resources

Triangles differentiated on the basis of their sides

Equilateral Triangles:

  A triangle with all sides equal to one another is called an equilateral triangle.

Isosceles Triangle:

A triangle with a pair of equal sides is called an isosceles triangle.


Scalene Triangle:

A triangle in which all the sides are of different lengths and no two sides are equal, the triangle is called a scalene triangle.

Triangles differentiated on the basis of their angles.

Acute angled triangle.

A triangle whose all angles are acute is called an acute-angled triangle or simply an acute triangle.


Right angle triangle

  A right triangle has one angle 90°

Right Isosceles Triangle

  If a triangle has a right angle (90°), and also two equal angles, can you guess what the equal angles are?

The Obtuse Triangle

  The Obtuse Triangle has an obtuse angle (an obtuse angle has more than 90°). In the picture on the left, the shaded angle is the obtuse angle that distinguishes this triangle. Since the total degrees in any triangle is 180°, an obtuse triangle can only have one angle that measures more than 90°.

* for geogebra link on types of triangles [click here ]

Angles in a triangle

Interior angles of a triangle

The interior angles are those on the inside of the triangle.  

Exterior Angles of a triangle

An exterior angle is formed by extending any side of the triangle.  

Image Acknowledgement: