 | Charles Sanders Peirce - Philosophy - 1997 - 322 pages
...any at all, that will bear being extended to the most extreme cases. Even that invaluable rule that the sum of the angles of a plane triangle is equal to two right angles shows signs of breaking down when by the aid of photometric considerations and that of the numbers... | |
 | Giandomenico Sica - Mathematics - 2006 - 270 pages
...therefore, the foundation of the most general geometry, since they do not depend on the assumption that the sum of the angles of a plane triangle is equal to two right angles" [Bonola (1955), pp. 93-94]. Although Lobachevsky had no reason to suspect that his geometry was not... | |
 | William Byers - Mathematics - 2010 - 424 pages
...does the existence of a proof for a mathematical proposition make it true in any absolute sense? Take the proposition that the sum of the angles of a plane triangle is two right angles. Is this an absolute or is it relative truth? The modern answer to this question is... | |
 | Richard Olson - Europe - 2008 - 370 pages
...still so.... A very absurd proposition may be very precise; as if we should say, for instance, that the sum of the angles of a [plane] triangle is equal to three right angles; and a very certain proposition may be wanting in precision in our statement of... | |
 | Sir Norman Lockyer - Electronic journals - 1905 - 1048 pages
...On the generalisation of an elementary theorem '< gi-ometry : H. Poincare. The theorem that the sum the angles of a plane triangle is equal to two right angles js extended to the case of the tetrahedron. — On ""lie theorems relating to algebraic surfaces of... | |
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He had demonstrated, unaided by any book or teacher, the proposition, that the sum of the angles of a plane triangle is equal to two right angles. 
