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Euclid, a great mathematician, wrote the first systematic textbook on geometry.

Euclid

Euclid, a great mathematician, wrote the first systematic textbook on geometry.

"A piece of a parallelogram left after a similar parallelogram has been removed from a corner of it. Thus, in the figure, EFGBCD is a gnomon." -Whitney, 1911

Gnomon

"A piece of a parallelogram left after a similar parallelogram has been removed from a corner of it.…

Illustration used to prove the Pythagorean Theorem, according to Euclid. A perpendicular is drawn from the top vertex of the right triangle extended through the bottom square, forming 2 rectangles. Each rectangle has the same area as one of the two legs. This proves that the sum of the squares of the legs is equal to the square of the hypotenuse (Pythagorean Theorem).

Euclid's Pythagorean Theorem Proof

Illustration used to prove the Pythagorean Theorem, according to Euclid. A perpendicular is drawn from…