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Pythagorean theorem. Arabic manuscript page showing a proof of the Pythagorean theorem by Persian polymath and mathematician Nasir al-Din Tusi (1201-1275). This theorem, named for 6th-century BC Ancient Greek mathematician Pythagoras, states that in a right-angled triangle, the sum of the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides. The proof shown here is that used by the Ancient Greek mathematician Euclid (circa 300 BC) as described in his work 'Elements'. This page is from Tusi's 'Euclid's geometry expounded' (1258).
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