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 242
be the centre of the sphere: join DB. DC, DA, and from Aon the straight lines DB, DC, draw the perpendiculars AE,AF; andfrom the points E and F, draw in theplane J)BC the straight lines EG, FGperpendicular to DB and DC, meetingone anotlier in G; join AG. Then, it may be proved, as was donein the… … 243 SPHERIC^i- TRIGONOMETRY. with the plane DBC. But because the spherical angles ACB, ABCare equal, the angles which the planes DAC, D AB make with theplane DBC are equal, (3. <ief.), and therefore the angles AFG, AEGare also equal. The triangles AGE,AGF have therefore two anglesof the one…
Euclid's Elements · Geometry · Trigonometry
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