EUCLIDE was an important mathematician in the ancient Greece and certainly one of the most acknowledged of every time and place. He is well known especially as author of Elements, fundamental work for the geometry of antiquity ; however, we know very little about his life. There are testimonies of his activity in Alexandria during Tolomeo I reign (323-283 a.C). In his masterpiece Elements he formulated the first complete and organic representation of geometry. The work is divided in 13 books in which he enunciates and demonstrates 465 Propositions and Theorems, not counting Lemmas, Corollaries and other Propositions contained in his other works. These are the Theorems that made him famous:
FIRST EUCLID THEOREM: « In a right-angled triangle the cathetus is proportional to the hypotenuse and the projection of the cathetus to the hypotenuse »
SECOND EUCLID THEOREM: « in a right-angled triangle, the square built on the height relative to the hypotenuse is equivalent to the rectangle that has on its sides the projections of the two cathets on the hypotenuse. ».