If the faces be all equal equilateral triangles the solid is termed the "regular" tetrahedron.
If there were such a thing as a triangle contained by absolutely straight lines, its three angles would no doubt measure what Euclid says; but straight lines and true triangles nowhere exist in reruns natura.
The arc measured was 3° 7' 3" in length; and the work consisted of two measured bases connected by a series of triangles, one north and the other south of the equator, on the meridian of Quito.
Contains problems of finding rational right-angled triangles such that different functions of their parts (the sides and the area) are squares.
Arrangements connected with Claus' formula are obtained by placing six tetrahedra on the six triangles formed by the diagonals of a plane hexagon.