One of the first lessons taught in school geometry classes was to learn the names of the different types of triangles that we can find, according to their sides or according to the gradation of their angles.
However, over time, these types of basic notions are forgotten or concepts are mixed due to lack of practice or application in real life. For this reason, today we will go back to our school days to review the types of triangles and their outstanding characteristics.

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What is a triangle
Before detailing the types of triangle, we should refresh our memory to define well what a triangle is.
The triangle is the flat polygon with fewer sides that we find in geometry, three in total. Consequently, its vertices and internal angles will also be three. These last ones, added, give a total of 180º, that is, a straight line if we open the figure.
The parts in which the triangle is divided are:

Vertices
These are the three points that shape the polygon, something that when represented uses the capital letters A, B and C.

Height
The height of the triangle is the distance from any of its sides with respect to the opposite vertex.

Base
It refers to any of the three sides of the triangle.

Sides
The sides are the sections that join two correlative vertices in a polygon. As we said, all types of triangle have three sides and, based on their length, their classification will be made.

Criteria to classify the types of triangles
We can find two different ways to classify the types of triangles depending on two criteria: the length of its sides or according to its angles.
Thus, considering the sides, the types of triangles are called ‘equilateral’, ‘isosceles’ and ‘scalene’; while according to their angles, these are ‘rectangles’, ‘acute angles’, ‘obtuse angles’ and ‘equiangles’.

3 types of triangles according to their sides
As we said in the previous point, the classification of triangles according to their sides is as follows:

1. Equilateral triangle
The three sides of this type of triangle are all the same length, so their angles internal will also be the same (60 degrees all three, 180 in total). To calculate the area of ​​this triangle we have to take the root of 3 , divide it by 4 and multiply by the length of the side squared.

2. Isosceles
triangle The isosceles triangle has two equal sides and one shorter side, so two of its angles will also have the same degrees.

3. Scalene triangle
Finally, the scalene triangle does not have any of its equal sides,they all have different length ; so that their angles will also differ from each other.

4 types of triangles according to the angles
Another consideration when classifying the types of triangles is taking into account their angles. So, these will be:

1. Rectangle Right
triangles owe their name to the fact that one of their interior angles is right, ergo it measures 90º.
The sides of the right triangle are called:

• Catetos : the shorter sides of the triangle, which between the two constitute the right angle.
• Hypotenuse : the side that is opposite the right angle. By its nature, it is the longest side in a right triangle.

If we want to calculate the area of ​​the right triangle, we must multiply the length of the two legs that form the right angle and divide the result by two.

2. Acute Angle
The particularity of this type of triangle is that none of its three angles reaches 90º .

3. Obtuse
triangles Those with two acute angles (90º) and one angle greater than 90º but less than 180º are called ‘obtuse triangles’.

4. Equiangle
This is another name given to the equilateral triangle if we look at its angles instead of the length of its angles. Having all the equal sides, also its three internal angles will be 60º.
If we hypothetically unfolded this triangle in the plane, we would see that the sum of its three angles results in 180º, that is, a straight line.

What is the use of knowing what types of triangles there are
“Well, but what is the use of knowing these geometric figures
? Is there any kind of use in knowing what the different types of triangle are
?” There are many doubts about whether the lessons that teachers taught us during school could have some kind of application in real life.
However, knowledge in geometry (among which we include knowing how to distinguish the types of triangles according to their sides or angles), are useful for disciplines such as technical drawing, for the planning of a work and its subsequent construction and even for a market in boom as is that of 3D printing.
Without going any further, physicists agree that, thanks to their shape, triangles have greater firmness compared to other types of figures ; an advantage that can and is used in architecture and engineering for the design of structures that have to support a lot of weight: roads, roofs, viaducts or overpasses, among others.

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