**Pythagorean Theorem**

Relationship between the measures *a*, *b* and *c* of the sides of a right triangle: : *a*^{2}* = b*^{2}* + c*^{2}, where *a* represents the length of the hypotenuse, and *b* and *c* the lengths of the two sides of the right angle.

### Historical note

With a modern perspective, we would be tempted to affirm that Pythagoras (Πυθαγó-ρας, meaning “announced by the Pythia”) was in his time a guru, thought leader, model, accomplished Olympian athlete, first philosopher, pedagogue, mathematician, musician. He was at the same time adulated by the disciples from his school and hated by the politicians who have chased him and ordered the destruction of all the buildings that housed his school. He can also be considered as a guru because of the secret and sectarian character of the Pythagorean school where everything was put in common, where the knowledge was attributed to the master, where like an initiatory organization, the members must go through different hierarchical degrees, such as *postulant*, *neophyte*, *akousmatikoi* (auditor ), then *mathēmatikoi* (scholar).

The symbol used by the followers of the Pythagorean school to recognize between themselves was the pentagram or the regular star pentagon.