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 241
e are equal. Let ABC be a spherical triangle, having the side AB equal to theside AC; the spherical angles ABC and ACBare equal. Let D be the centre of the sphere;join DB, DC, DA, and from A on thestraight lines DB, DC, draw the perpen-diculars AE, AF; and from the pointsE and F draw in the plane… … SPHERICAL TRIG01j:OMETRY. 241 passes through AE, EG (4. 2. Sup.); and tlierefore, every planethat passes through DE is at right angles to the plane AEG (17. 2.Slip.); wherefore, the plane DBC is at right angles to the planeAEG. For the same reason, the plane DBC is at right angles to theplane AEG,…
Euclid's Elements · Geometry · Trigonometry
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