A deltahedron
The definition of regular polyhedron doesn’t require only the equality and regularity of the polygons of the faces: in the photo you can see one of the five convex polyhedra (deltahedra) that are not regular polyhedra, but have this property. You can see also a net.
© matematita
The image belongs to the sections...:
Deltahedra (3D geometry)
Prisms, antiprisms, pyramids, dipyramids (3D geometry)
