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Octahedron
The ancient Greeks gave the polyhedron a name by the number of faces. "Octo" means eight, "hedra" means the face (octahedron - a solid with eight faces).
Therefore, the question - "what is an octahedron?", We can give the following definition: "An octahedron is a geometric solid of eight faces, each of which is a right triangle."
The polyhedron belongs to regular polyhedra and is one of the five Platonic solids.
The octahedron has the following characteristics:
The face type is a regular triangle;
The number of sides at the verge - 3;
The total number of faces is 8;
The number of edges adjacent to the top is 4;
The total number of vertices is 6;
The total number of edges is 12;
The regular octahedron is composed of eight equilateral triangles. Each vertex of the octahedron is a vertex of four triangles. Therefore, the sum of flat angles at each vertex is 240 °.
The octahedron has a center of symmetry - the center of the octahedron, 9 axes of symmetry and 9 planes of symmetry.
The octahedron can be represented as two regular pyramids with a quadrilateral base connected to each other through this base.
The octahedron can be placed in a sphere (inscribed), so that each of its vertices will touch the inner wall of the sphere. The radius of the described sphere of the octahedron is determined by the formula: , where "a" is the side length. The sphere can be inscribed inside the octahedron. The radius of the octahedron inscribed sphere is determined by the formula: The surface area of the octahedron The surface area of an octahedron can be represented in the form of a net area. The surface area can be defined as the area of one of the sides of the octahedron (this is the area of a regular triangle) multiplied by 8. Or use the formula: The volume of the octahedron is determined by the following formula:
The octahedron can be made by yourself. Paper or cardboard is the most suitable option. For the assembly will require paper net - a single part with the lines of the folds. The ancient Greek philosopher Plato associated the octahedron with the "earth" element - air, therefore, to build a model of this regular polyhedron, we chose gray. The figure shows the octahedron sweep: Note that this is not the only sweep option. To build a model, you can download a net in pdf format and print it on an A4 sheet: The classic version of the coloring involves the color of the octahedron in four different colors, and in such a way that each face has its own color different from the next and only the opposite faces that are not in contact with each other are painted in the same color. Coloring option is presented in the figure. You can download the net with the appropriate coloring of the faces.
Mathematical characteristics of the octahedron
Octahedron nets
- if you print on a color printer - color net.
- if you use color cardboard for assembly - net.
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