a, b, c - length of edges of a base. H - height. The triangular pyramid has 4 faces, 6 edges, 4 vertices. Angles in triangular pyramid. S = a^2√3, V = a^3√2. The tetrahedron has four faces which are equilateral triangle. The regular triangle pyramid has in base equilateral triangle and its height drop directly onto center of the base. All three lateral faces of this pyramid are isosceles triangles. The volume and the surface find in the same way as all pyramids: V = 1/3 * A_b * H, S = A_b + A_f. H - height. A_b - area of a base (triangle). A_l - lateral area (sum of areas of triangles).