Elements of geometry : containing the first six books of Euclid, with a supplement on the quadrature of the circle, and the geometry of solids : to which are added, Elements of plane and spherical geometry (1826)
Playfair, John, 1748-1819, Euclid · Philadelphia : Marot & Walter · leaf 255
SPHERICAL TRIGONOMETRY. i 255 PROP. XXVIII. The same construction remaining, the cosines of these8:!rients of the vertical a,ngle are recipjEOcally proportionaltQ the tangents of th,e sides. Because (21.), cos. BCD : R .. tan. CD : tati. BC, and also, cos.AC I) : H .. tan. CI) : tan. iVC, by…
Euclid's Elements · Geometry · Trigonometry
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