Examples of analytical geometry of three dimensions

"Let 0A, 0B, 0C be three edges of a rectangular parallelepiped which meet at a point 0; take 0 for the origin and the directions of 0A, 0B, 0C for the axes of x, y, z respectively; complete the parallelepiped; let D be the vertex opposite to A, E that opposite to B, F that opposite to C, G that opposite to 0."