Legendre, A. M. (Adrien Marie), 1752-1833, Brewster, David, Sir, 1781-1868, Davies, Charles, 1798-1876 · New York, Wiley & Long · leaf 202
GEOMETRY. have DQF+FQE—DQE-APC + CPB^APB, or DFE=: ABC ; hence the two symmetrical triangles ABC, DEF areequal in surface. Scholium, The poles P and Qmight lie within triangles ABC,DEF: in which case it would berequisite to add the three trianglesDQF, FQE, DQE, together, in or-der to make up the… … 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.
Trigonometry · Geometry
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