Pythagorean Theorem

Pythagorean The­o­rem: In a right angled tri­an­gle: the square of the hypotenuse is equal to the sum of the squares of the other two sides.

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the Pythagorean theorem!
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The­o­rem (Boyaj, 1832; Gervin, 1833).

If two poly­gons have the same area, then they are decom­pos­able in the same set of poly­gons.

That is, if two poly­gons have equal areas, then any of them can be decom­posed into a finite set of pieces with which it is pos­si­ble to recon­struct exactly the other poly­gon.