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 219
EL is the cosine of AC, and EH of AB, FK isthe sum of these cosines, and KB their difference; for FK=4 FB-fEL=EH+EL, and KB=LH=EH—EL. Now, FK : KB .*: tan.FDKrtan. BDK; and tan. FDK=cotan. DFK,because DFK is thecomplement of FDK; therefore, FK : KB *.: cotan.DFK: tan.BDK,that is, FK : KB II cotan.… … Cor. 2. In the right angled triangle FKD, FK : KD II R ; tan.DFK: Now FK=co8. AB-fcos. AC, KD=sin. AB-f sis., AC, and PLANE TRIGONOMETRY. 21d tan. DFK=taTi. I (AB+AC), therefore cos. AB+coa. AC : sin.AB+siu. AC :: R : tan. k (AB+AC). In the same manner, by help of the triangle FKC, it may be…
Euclid's Elements · Geometry · Trigonometry
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![An illustration from Nicolai Copernici Torinensis De reuolutionibus orbium coelestium, libri VI : Habes in hoc opere iam recens nato, & aedito, studiose lector, motus stellarum, tam fixarum, quàm erraticarum, cum ex ueteribus, tum etiam ex recentibus obseruationibus restitutos: & nouis insuper ac admirabilibus hypothesibus ornatos. Habes etiam tabulas expeditissimas, ex quibus eosdem ad quoduis tempus quàm facillime caculare poteris. Igitur eme, lege, fruere. [Line in Greek] (1543)](https://img.insideoutlibrary.com/img/200/ia-nicolaicopernici00cope-319-211.webp)
