A treatise on special or elementary geometry (1877)
Olney, Edward, 1827-1887, Olney, Edward, 1827-1887. Elements of trigonometry, plane and spherical · New York : Sheldon · leaf 134
of the n angles, there is aninterior and an exterior angle, whose sum, asA + a, is two right angles. Hence the sum ofall the exterior and interior angles is n times tworight angles. Now, from this sum subtractingthe sum of the exterior angles, the remainderis the sum of the interior angles. But, by… … OF REGULAR POLYGONS* PROPOSITION xrn. 258. Tlieorem.—The angles of an inscribed equilateral polygonare equal; and the polygon is regular, Dem.—Let ABCDEF be an inscribed polygon, with AB = BC = CD,etc.:then is angle A = B = C = D, etc., and the polygon is regular. For,from the centre of the circle…
Geometry · Trigonometry
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