De Gua's Theorem

De Gua's theorem is a three-dimensional analog of the Pythagorean theorem, named after the French mathematician Jean Paul de Gua de Malves. It states that if a tetrahedron has a right-angle corner, like the corner of a cube, then the square of the area of the face opposite that corner equals the sum of the squares of the areas of the tetrahedron's other three faces. The theorem can also be used to prove a special case of Heron's formula. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/