The notion of diagonal, with etymological origin in the Latin word *diagonālis*, is used to refer to the straight line that allows joining two vertices that are not contiguous of a polyhedron or a polygon.

The diagonals appear as segments or lines that have a certain inclination. Suppose that, in a square, vertices A and B are located at the endpoints of the upper side (A on the left and B on the right), while vertices C and D are located at the endpoints of the lower side (C below). from A and D below B). Inside this square, we will find two diagonals: AD (which goes from A to D) and CB(extending from C to B). These diagonals are perpendicular to each other.

A diagonal is a line that shows a certain inclination. See Abbreviation Finder for acronyms related to diagonal.

## The etymological origin

By studying the etymology of the term *diagonal*, we discover that its origin is found in the Greek language, precisely in the word *diagonios*, which can be translated as “sack”. The geographer Strabo and the mathematician Euclid, two essential characters in the evolution of science in general, spoke of *diagoniums* to refer to the segment that joins two vertices of a cuboid or rhombus.

At first glance, we notice that the components of this Greek word are the following: the prefix *dia-*, which indicates “across”, and the term *gonia*, which can be translated as “ angle ” and is related to *gony*, defined as “knee”. »; the idea, therefore, was “(a line that) passes through the angles.” It came to Latin as *diagonus and then diagonalis* emerged.

In the game known as tatetí or three in a row, you can win the game by lining up diagonally.

## Diagonal and polygon

The Greek word *gonia* has also given us the element *-gono*, which in our language is used to describe various flat figures in the field of geometry, which we call *polygons*, among which are *decagon, dodecagon, hendecagon, enneagon, heptagon, hexagon, octagon, pentagon, pentadecagon, tetragon, trine,* and *undecagon*.

Given any polygon, to find out the number of diagonals that can be drawn inside it, that is, between its vertices, we must solve the following equation: Nd = n(n – 3) / 2, where Nd is “number of diagonals” and n, “number of sides”. In the case of a tetragon (also called a *quadrilateral*, since it has four sides as well as four angles), the result would be 2, since 4(4 – 3) / 2 = 2.

Taking into account the same criterion expressed so far, it is possible to distinguish between upper and lower secondary diagonal, depending on whether we are talking about the elements that are directly above or below the main diagonal, respectively.

According to the work of Pythagoras, we can say that the diagonal of a rectangle, taking into account two of its contiguous sides, allows us to find an equality that in one term has the diagonal squared and in the other, the sum of the squares From both sides. If the diagonal belongs to a rectangular cuboid, the sum of the squares of three concurrent edges at a vertex is equal to the square of the diagonal.

## A type of street and the name of a newspaper

In the urban framework, the avenue or street that obliquely cuts other arteries that are parallel to each other is called diagonal. The Spanish city of Barcelona, for example, has Diagonal Avenue, which divides the Ensanche district diagonally into two parts.

Lima, in Peru, also has a Diagonal avenue. In the City of Buenos Aires, on the other hand, Presidente Roque Sáenz Peña avenue is recognized as Diagonal Norte, while Presidente Julio Argentino Roca avenue is called Diagonal Sur.

*“Diagonal”*, finally, is the name of a Spanish newspaper founded in 2005. It is a publication of progressive ideology that usually includes criticism of the capitalist system.