# Pythagorean theorem

- The Editors of Encyclopædia Britannica

**Pythagorean theorem**, the well-known geometric theorem that the sum of the squares on the legs of a right triangle is equal to the square on the hypotenuse (the side opposite the right angle)—or, in familiar algebraic notation,

*a*

^{2}+

*b*

^{2}=

*c*

^{2}. Although the theorem has long been associated with Greek mathematician-philosopher Pythagoras (

*c.*570–500/490 BCE), it is actually far older. Four Babylonian tablets from circa 1900–1600 BCE indicate some knowledge of the theorem, or at least of special integers known as Pythagorean triples that satisfy it. The theorem is mentioned in the Baudhayana

*Sulba-sutra*of India, which was written between 800 and 400 BCE. Nevertheless, the theorem came to be credited to Pythagoras. It is also proposition number 47 from Book I of Euclid’s

*Elements*.

According to the Syrian historian Iamblichus (*c.* 250–330 CE), Pythagoras was introduced to mathematics by Thales of Miletus and his pupil Anaximander. In any case, it is known that Pythagoras traveled to Egypt about 535 BCE to further his study, was captured during an invasion in 525 BCE by Cambyses II of Persia and taken to Babylon, and may possibly have visited India before returning to the Mediterranean. Pythagoras soon settled in Croton (now Crotone, Italy) and set up a school, or in modern terms a monastery (*see* Pythagoreanism), where all members took strict vows of secrecy, and all new mathematical results for several centuries were attributed to his name. Thus, not only is the first proof of the theorem not known, there is also some doubt that Pythagoras himself actually proved the theorem that bears his name. Some scholars suggest that the first proof was the one shown in the figure. It was probably independently discovered in several different cultures.

B. A. Operations Research & Statistics, California State University, Long Beach, Teaching Assistant undergraduate Mathematics. B.S. Mathematics, California State University, Long Beach. Mathematics University of California, Irvine, Teaching Assistant undergraduate Mathematics. Completed course work for MS Degree with 4.0 GPA. M.S. Mathematics, Kingsbridge University. Transcript available upon request. 1988-Present: Mathematics tutoring--One on one tutoring for SES students through YP institute and Academic advantage. Tutored students with low learning skills as well as very bright students. Tutored groups of four students in math classes from basic mathematics through calculus. Mathematics teaching for EFN, Inc., a private school.

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