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 125
because AC is parallel to FE, one of the sides of the triangleFBE,BA: AF - BC : CE (2. 6^: but AF is equal to CD; there-fore (7. 5.), BA : CD :: BC : CE; and alternately, BA : BC : DC•• CE (1«. 5.): Again, because CD is parallel to BF, BC : CE **FD : DE (2. 6.); but FD is equal to AC; therefore BC… … PROP. V. THEOR. If the sides of two triangles, about each of their angles^be proportionals, the triangles shall be equiangular, andhave their equal angles opposite to the homologous sides. Let the triangles ABC,DEF have their sides proporlionals, so thatAB is to BC, as DE to EF; and BC to CA, as EF…
Euclid's Elements · Geometry · Trigonometry
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