Introduction to Types of Triangles in Geometry

In geometry, we learn different types of shapes and sizes. Based on dimensions, these shapes are defined as one-dimensional, two-dimensional and three-dimensional. In this article, we will learn about different types of triangles. But before we move ahead, first let us have a quick review of the basics of the triangle. 

A triangle is a two-dimensional figure that has three sides and three vertices. It is a closed shape that is formed by three line segments, whose ends are connected to each other through a node, called the vertex. An example of a triangle is an equilateral triangle, with three equal sides. Each vertex forms the angle of the triangle. The sum of any two sides of a triangle is always greater than the third side. Also, the sum of all the interior angles of a triangle is equal to 180 degrees. All these properties are true for all types of triangles. Now let us see what these triangles are.


Usually, there are six types of triangles in geometry. Again these six types are categorised into two categories.

  • Based on the measure of angles of a triangle
  • Based on the sides of the triangle

We should begin with the three types of triangles that are ordered by the proportion of their biggest angle. These are the acute, right, and obtuse triangles. Yet, how would you realise which will be which? Find the biggest angle of every triangle and note whether or not the angle is more than, less than, or equivalent to 90 degrees.

Acute Triangle

A triangle whose all three interior angles are less than 90 degrees is called the acute triangle. For example, a triangle with its three angles 70 degrees, 50 degrees and 60 degrees is an acute triangle. 

70 + 50 + 60 = 180

Right triangle

When the measure of any one of the angles in a triangle is equal to 90 degrees, then such a triangle is called a right triangle. A right triangle can have angles equal to 90 degrees, 45 degrees and 45 degrees, since the sum of the three angles is 180 degrees.

90 + 45 + 45 = 180

Obtuse Triangle

If the measure of any one of the angles of a triangle is greater than 90 degrees, then the triangle is known as an obtuse triangle. For example, a triangle with angle measures 32 degrees, 31 degrees and 117 degrees is an obtuse triangle.

32 + 31 + 117 = 180

The above three sets of triangles were based on angles. Now our second set of triangles is based on the length of sides. Let us have a brief look at them.

Scalene Triangle

A scalene triangle is a triangle that has all its three sides unequal in length. Hence, no sides are equal to each other. This also concludes that the angles of the scalene triangle will also be of different measures.

Isosceles Triangle

A triangle that has any two sides of equal length is called an isosceles triangle. Also, the opposite angles of equal sides are equal in measure for an isosceles triangle. 

Equilateral Triangle

From the above two types of triangles, you may have guessed that the third type of triangle will be a triangle that will have all its three sides equal in length. Again, if the three sides are equal, then the measure of three angles will also be equal. 

After learning the classification of triangles, the difference between each of these triangles has been understood now, and we can also solve the problems based on them. 

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