Legendre, A. M. (Adrien Marie), 1752-1833, Brewster, David, Sir, 1781-1868, Davies, Charles, 1798-1876 · New York, Wiley & Long · leaf 202
PROPOSITION XIX. THEOREM. If the circumferences of two great circles intersect each other onthe surface of a hemisphere, the sum of the opposite trianglesthus formed, is equivalent to the surface of a lune whose angleis equal to the angle formed by the circles. … Let the circumferences AOB, COD,intersect on the hemisphere OACBD ;then will the opposite triangles AOC,BOD, be equal to the lune whose an-gle is BOD. For, producing the arcs OB, OD, onthe other hemisphere, till they meet inN, the arc OBN will be a semi-circum-ference, and AOB one also ; and…
Trigonometry · Geometry
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![An illustration from Nicolai Copernici Torinensis De reuolutionibus orbium coelestium, libri VI : Habes in hoc opere iam recens nato, & aedito, studiose lector, motus stellarum, tam fixarum, quàm erraticarum, cum ex ueteribus, tum etiam ex recentibus obseruationibus restitutos: & nouis insuper ac admirabilibus hypothesibus ornatos. Habes etiam tabulas expeditissimas, ex quibus eosdem ad quoduis tempus quàm facillime caculare poteris. Igitur eme, lege, fruere. [Line in Greek] (1543)](https://img.insideoutlibrary.com/img/200/ia-nicolaicopernici00cope-149-83.webp)
