An octahedron is a polyhedron with 8 faces. A regular octahedron is composed of eight equilateral triangles. The horizontal section of an octahedron is a square and the vertical section is a square too. These squares are congruent.
A diagonal of octahedron is a diagonal of one of those squares:
d = a √ 2
where: a = 5 cm
Answer: d = 5 √ 2 cm
