STEP 3: Three regular triangles on a corner make a tetrahedron, four make an octahedron and five make an icosahedron. Six triangles make a flat sheet that can't be folded into a corner.

A 3D shape with all straight edges and flat faces is a polyhedron ... dodecahedron and icosahedron. A prism is a 3D shape with a constant polygon shaped cross-section. A prism is named by the ...