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** what **they are not contiguous** of a polyhedron or a polygon.

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

In the urban framework, the diagonal is called **avenue** wave **Street** which cuts obliquely to other arteries that are parallel to each other. The Spanish city of **Barcelona** , for example, has the **Diagonal Avenue** , which divides the district from **Expansion** diagonally in two parts. **Lime** , in **Peru** , also has a **Diagonal Avenue** . In the **Buenos aires city** , on the other hand, to the avenue **President Roque Sáenz Peña** It is recognized as **North Diagonal** while the **President Julio Argentino Roca Avenue** receives the denomination of **South Diagonal** .

** "Diagonal"** Finally, it is the name of a

**Newspaper**Spanish founded in

**2005**. It is a publication of progressive ideology that usually includes criticism of the capitalist system.

When studying the etymology of the term *diagonal*, we discover that its origin is in the Greek language, precisely in the word *heck*, which can be translated as "sack". The geographer **Strabo** and the mathematician **Euclid** , two essential characters of the evolution of science in general, talked about *heck* to refer to **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 *day-*, which indicates "through", and the term *gonia*, which can be translated as "**angle** "and relates to *gony*, defined as "knee"; the idea, therefore, was "(a line that) passes through the angles." Latin came as *diagonus* and then arose *diagonalis*.

The Greek word *gonia* He has also given us the element *-gono*, which in our language is used for the description of various flat figures in the field of **geometry** , what we call *polygons*, among those found *Decagon, Dodecagon, Decagon, Entagon, Heptagon, Hexagon, Octagon, Pentagon, Pentadecagon, Tetragon, Trine* and *undecagon*.

Given a **polygon** Anyone, to find out the number of diagonals that can be drawn inside, that is, between their 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 (which is also called *quadrilateral*, since it has four sides, in addition to four angles), the result would be **2** , as **4(4 - 3) / 2 = 2** .

Taking into account the same **criterion** expressed so far, it is possible to distinguish between **upper secondary diagonal** and **lower** , as 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 adjacent sides allows us to find an equality that in one term has the diagonal squared and in the other, the sum of the squares of both sides. If the diagonal belongs to a rectangular orthohedron, the sum of the squares of three concurrent edges at a vertex is equal to the square of the diagonal.