‘The Greeks recognized that there are only five platonic solids. But why is this so? The key observation is that the interior angles of the polygons meeting at a vertex of a polyhedron add to less than 360 degrees.’ (Read more: http://en.wikipedia.org/wiki/Platonic_solid ; July 26, 2012).

A polygon is said to be regular if the edges are of equal length and meet at equal angles. A polygon is convex if the line connecting any two points inside the polygon is itself entirely inside the polygon.

Plate5 Tetrahedron (Four Vertexes /Four Faces)

(Source : http://www.google.co.in/search?num=10&hl=en&site=imghp&tbm=isch&source=hp&biw
=1328&bih=574&q=Application+of+Tetrahedron+in+Products&oq=Application+of+Tetrahedron+in+
Products&gs_l=img.12...186971.215810.1.217597.38.12.0.26.26.0.181.1497.1j11.12.0...0.0...1ac.
5xzfmwhWe3o#hl=en&site=imghp&tbm=isch&sa=1&q=Tetrapack&oq=Tetrapack&gs_l=img.12...3
3141.39123.2.422411.11.0.0.0.0.0.0..0.0...0.0...1c.xeqt65P0szA&pbx=1&bav=on.2,or.r_gc.r_pw.r_
qf.,cf.osb&fp=6304bec68e605024&biw=1328&bih=574 ; July 31, 2012)

Exercise #02: Make a Tetrahedron and create graphic design on all faces maintaining the character of the surface planes.  

The simplest of these shapes is the Tetrahedron (plate5), a four-sided faces solid bounded by equilateral triangles on all sides having four vertexes. Packaging industry widely uses the principle of tetrahedron for various products.