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Euclid is a greek mathematician. He is known as the "Father of Geometry". He wrote the Elements. This book consisted of his five postulates. He based all of his theorems off of these postulates. This book became one of the most famous books in mathematics. It is still used today to teach and learn about mathematics. The Elements have been studied for 24 centuries in different languages. Euclid wrote a proof of the Pythagorean Theorem that is different then above. This just shows that there is more then one way to solve the Pythagorean Theorem. I have included below Euclid's proof of the Pythagorean Theorem, and an interactive site to explore Euclid's Elements if you'd like to learn more about them!
Euclid's Proof of the Pythagorean Theorem