A diagonal is a straight line that shows a certain inclination.
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.
Diagonals appear as segments or lines that have a certain inclination . Suppose that, in a square , vertices A and B are located at the extremes of the upper side ( A on the left and B on the right), while vertices C and D are located at the extremes of the lower side ( C below of A and D below B ). Inside this square, we will find two diagonals: AD (which runs from A to D ) and CB (which extends from C to B ). These diagonals are perpendicular to each other.
The etymological origin
When studying the etymology of the term diagonal , we discovered 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 figures in the evolution of science in general, spoke of diagonios 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 "through", 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 tic-tac-toe, you can win the game by achieving a diagonal alignment.
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, trigon 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 (which is also called a quadrilateral , since it has four sides, in addition to 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 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. 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 fabric, the avenue or street that cuts obliquely to other arteries that are parallel to each other is called diagonal. The Spanish city of Barcelona , for example, has Diagonal Avenue , which divides the Eixample district diagonally into two parts.
Lima , in Peru , also has a Diagonal avenue . In the City of Buenos Aires , on the other hand, Avenida Presidente Roque Sáenz Peña is recognized as Diagonal Norte , while Avenida Presidente Julio Argentino Roca is called Diagonal Sur .
«Diagonal» , finally, is the name of a Spanish newspaper founded in 2005 . It is a publication with a progressive ideology that usually includes criticism of the capitalist system.