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 252
BC. Q. E. D. PROP. XX. In right angled spherical triangles, the cosine of thehypotenuse is to the radius as the cotangent of either ofthe angles is to the tangent of the remaining angle. Let ABC be a spherical triangle, having a right angle at A, the co-sine of the hypotenuse BC is to the radius as… … the pole B, of the circle DF, DF must pass through the pole of BD,(4.). And since AC is perpendicular to BD, the plane of the circleAC is perpendicular to the plane of the circle BAD, and thereforeAC must also (4.) pass through the pole of BAD; wherefore, thepole of the circle BAD is in the point…
Euclid's Elements · Geometry · Trigonometry
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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-60-36.webp)
