Named for Plato, who theorized that the classical elements were made of these regular polyhedrons, three of the Platonic solids are composed of equilateral triangles: the tetrahedron, octahedron, and ...

The base and the perpendicular height are at right angles to each other. The measurements used must be in the same units. For example, to work in cm a 45 mm measurement would have to be converted to ...