The 7 Types Of Triangles: Classification According To Their Sides And Angles

A geometric shape that can be subdivided according to various characteristics.

During our childhood, we have all had to attend math classes at school, where we have had to study different types of triangles. However, as the years go by, we can forget some things that we have studied. For some individuals mathematics is a fascinating world, but others enjoy the world of letters more.

In this article we will review the different types of triangles, so it can be useful to refresh some concepts studied in the past or to learn new things that were not known.

Usefulness of triangles

In mathematics, geometry is studied, and delves into different geometric figures such as triangles. This knowledge is useful for many reasons; for example: to make technical drawings or plan a construction site and its construction.

In this sense, and unlike a rectangle that can be transformed into a parallelogram when force is applied to one of its sides, the sides of a triangle are fixed. Due to the rigidity of its shapes, physicists showed that the triangle can withstand high amounts of force without deforming. Therefore, architects and engineers use triangles when building bridges, roofs on houses, and other structures. When triangles are built into structures, resistance increases by reducing lateral movement.

What is a triangle

The triangle is a polygon, a flat geometric figure that has area but no volume. all triangles have three sides, three vertices and three interior angles, and the sum of these is 180º

The triangle is made up of:

  • Vertex : each of the points that a triangle determines and that are usually indicated by uppercase Latin letters A, B, C.
  • Base : it can be any of its sides, the opposite of the vertex.
  • Height : is the distance from one side to its opposite vertex.
  • Sides : there are three and because of these, triangles are usually classified in different ways.

In these figures, one of the sides of this figure is always less than the sum of the other two sides, and in a triangle with equal sides, its opposite angles are also equal.

How to find the perimeter and area of ​​a triangle

Two measurements that we are interested in knowing about triangles are the perimeter and the area. To calculate the first, it is necessary to add the lengths of all its sides:

P = a + b + c

Instead, to find out what the area of ​​this figure is, the following formula is used:

A = ½ (bh)

Therefore, the area of ​​the triangle is base (b) times height (h) divided by two, and the resulting value of this equation is expressed in square units.

How triangles are classified

There are different types of triangles, and they are classified taking into account the length of their sides and the width of their angles. Taking into account its sides, there are three types: equilateral, isosceles and scalene. Based on their angles, we can distinguish right, obtuse, acute, and equiangular triangles.

We go on to detail them below.

Triangles according to the length of their sides

Taking into account the length of the sides, the triangles can be of different types.

1. Equilateral triangle

An equilateral triangle has three sides of equal length, making it a regular polygon. The angles in an equilateral triangle are also equal (60º each). The area of ​​this type of triangle is the root of 3 by 4 times the length of the side squared. The perimeter is the product of the length of one side (l) and three (P = 3 l)

2. Scalene triangle

A scalene triangle has three sides of different lengths, and its angles also have different measures. The perimeter is equal to the sum of the lengths of its three sides. That is: P = a + b + c.

3. Isosceles triangle

An isosceles triangle has two equal sides and two angles, and the way to find its perimeter is: P = 2 l + b.

Triangles according to their angles

Triangles can also be classified according to the width of their angles.

4. Right triangle

They are characterized by having a right interior angle, with a value of 90º. The legs are the sides that make up this angle, while the hypotenuse corresponds to the opposite side. The area of ​​this triangle is the product of its legs divided by two. That is: A = ½ (bc).

5. obtuse triangle

This type of triangle has an angle greater than 90 ° but less than 180 °, which is called “obtuse”, and two acute angles, which are less than 90 °.

6. Acute triangle

This type of triangle is characterized by its three angles that are less than 90 °

7. Equiangular triangle

It is the equilateral triangle, since its internal angles are equal to 60 °.


Practically all of us have studied geometry in school, and we are familiar with triangles. But over the years, many people may forget what their characteristics are and how they are classified. As you have seen in this article, triangles are classified in different ways depending on the length of their sides and the width of their angles.

Geometry is a subject that is studied in mathematics, but not all children enjoy this subject. In fact, some have serious difficulties. What are the causes of this? In our article ” Children’s difficulties in learning mathematics ” we explain it to you. 

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