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 243
a great circle. Let ABC be a spherical triangle as before, the three sides AB, BC,AC are less than the circumference of a ?:reat circle. Let D be the centre of the sphere: The solid angle at D is con-tained by three plane angles BDA, BDC, ADC, which together areless than four right angles (21.2.…
Euclid's Elements · Geometry · Trigonometry
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