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 221
Otherwise, without the 3d. Let ABC be a triangle; the sum of AB and AC any two shies, isto the difference of AB and AC as the tangent of half the sum of theangles ACB and ABC, to the tangent of half their difference. 220 PLANE TRIGONOMETRY. About the centre A with the radius AB, the greater of the… … Because the exterior angle EAB is equal to the two Interior ABC,ACB, (32. 1.): and the angle EFB, at the circumference is equal tohalf the angle EAB at the centre (20. 3.); therefore EFB is half thesum of the angles opposite to the sides AB and AC. Again, the exterior angle ACB is equal to the two…
Euclid's Elements · Geometry · Trigonometry
Internet Archive · Public Domain Mark 1.0. Free to use for anything.
