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### The Pythagorean theorem

The triangle has a right angle and two acute angles. From this structure of angles, it is possible to calculate trigonometric ratios of these triangles. In this way, if in a triangle greater sides are 13 cm and 12 cm, it is possible to calculate the distance of the less acute angle by applying the Pythagorean theorem (in this case the end result would be one angle less than 25 degrees, because the Pythagorean theorem says that in a right triangle the square of the hypotenuse is equal to the sum of the squares of the legs).### Practical applications and presence of triangles

Pythagoras was born on the Greek island of Samos in the Vl century a. C. His theorem is a fundamental tool to calculate and solve real problems in all kinds of disciplines: architecture, urban planning, cartography, geography, etc. These and other theoretical disciplines allow to solve practical questions, since form having a right triangle can be found on the map of a city, in a ladder resting on the wall or on the angles there at a sports court.The concept of triangle becomes a reality in the daily life and, in fact, appears in all circumstances and situations (a roof of a House, a sculptor with a geometric shape or in the sail of a boat).

### Other triangles

All triangles have necessarily 3 points joined by segments. If we classify triangles according to their sides have an equilateral triangle with three equal sides, the isosceles has two equal sides, and scalenus does not have any side that is equal. Another way to classify triangles is given its angles. According to this classification, in addition to the aforementioned right triangle (recall that it presents a 90 degree angle), also exists the acute-angled triangle (all three angles are less than 90 degrees) and the obtuse-angled triangle (one angle is greater than 90 degrees).**Article contributed by the team of collaborators.**