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 218
. ^^^_1> PROP. II. The sides of a plane triangle are to one another as thesines of the opposite angles. From A any angle in the triangle ABC,let AO be drawn perpendicular to BC.And because the triangle ABD is rightangled at D, AB : AD : : R : sin. B; andfor the same reason, AC : AD : : R:sin. C,… … 218 PLANE TRIGOXOMETRY. PROP. III. • The sum of the sines of any two arches of a circle, is tothe difference of their sines, as the tangent of half the sumof the arches to the tangent of half their difference. Let AB, AC be two arches of a circle ABCD; let E be the ceiitre»and AEG tlie diameter…
Euclid's Elements · Geometry · Trigonometry
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