Online Geometry Problem 800: de Gua's Theorem, Pythagorean theorem in 3-D, Tetrahedron, Cubic Vertex,
Triangular Pyramid, Apex, Height, Right Triangle Area,
Base Area, Projected Area. Level: High School,
SAT Prep, College,
Mathematics Education

In any tetrahedron with a cubic vertex O-ABC the square of the area of the face opposite the cubic vertex O-ABC is equal to the sum of the squares of the areas of the other three faces AOB, AOC, BOC.