Elements of geometry and trigonometry. Revised and adapted to the course of mathematical instruction in the United States (1856)
Legendre, A. M. (Adrien Marie), 1752-1833, Davies, Charles, 1798-1876 · New York : A.S. Barnes · leaf 236
ON IV. TIIEOKEM. The angle formed hy two arcs of great circles, is equal to theangle formed hy the tangents of these arcs at their pointof intersection. The angle is measured hy the arc of agreat circle described from the vertex as a pole, and limiiedhy the sides, j^f^oduced if necessary. Let the… … For, tlie tangent AF, drawn in theplane of tlie arc AB, is perpendicular tothe radius A 0; and the tangent A G,drawn in the plane of the arc ACj isperiDcndicular to the same radius AO.Hence, the angle FAG is equal to theangle contained bj the planes ABDII,ACFII {b.yi.,I). 4:)] Avhich is that ofthe…
Geometry · Trigonometry
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