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 131
les re-ciprocally proportional, are equal to one another. Let AB, BC be equal paralle-lograms, which have the anglesat B equal, and let the sides DB,BE be placed in the same straightline; wherefore also FB, BGare in one straight line (14. 1.):the sides of the parallelogramsAB, BC, about the equal… … OF GEOMETRY. BOOK VI. 131 but because the parallelograms AB, FE have the same altitude,AB : fE :: DB : BE (l. 6.), also,BC : FE :: GB : BP (l. 6.); thereforeDB : BE :: GB : BF (ll. 15.). Wherefore, the sidesof the parallelograms AB, BC about their equal angles are recipro-cally proportional. IBut,…
Euclid's Elements · Geometry · Trigonometry
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