arch, and of the fum of the fines of the firft and third. Demonfiratw. Let the equi-difterent arches be A B, A C, & A D, then is B C the differencebetween A C and A B equal to C D the difference between A D and A C, and making F C e-qual to C A, if A D be extended to F, the angles CF D and B A… … the angles F D C and C B A are equal, and the triangles ABC and C F D arc equal alfo, bythe fourth of the firft of Euclid, and therefore C D being equal to C B, and F C to A C, bycon-ftruction, F D is alfo equal to A B, and F A is the fumme of A B and *AY). and the fquare ofA C is equal 10 the…
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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-401-278.webp)
