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The ancient Greeks gave the polyhedron a name according to the number of faces. "Tetra" means four, "hedra" means the face (tetrahedron - a solid having four faces).

Polyhedron refers to the regular polyhedra and is one of the five **Platonic solids**.

The tetrahedron has the following **characteristics**:

The type of face is the right triangle;

The number of sides at the face is 3;

The total number of faces is 4;

The number of edges adjacent to the vertex is 3;

The total number of vertices is 4;

The total number of edges is 6;

The regular tetrahedron is composed of four equilateral triangles. Each vertex is a vertex of three triangles. Therefore, the sum of flat angles at each vertex is 180 °.

The tetrahedron has no symmetry center but has 3 axes of symmetry and 6 planes of symmetry.

Is the tetrahedron a pyramid? Yes, the tetrahedron is a triangular pyramid where all sides are equal.

Can a pyramid be a tetrahedron? Only if it is a pyramid with a triangular base and each of its sides is an equilateral triangle.

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