The elements of Euclid : viz, the first six books, together with the eleventh and twelfth : the errors, by which Theon, or others, have long ago vitiated these books, are corrected, and some of Euclid's demonstrations are restored : also, The book of Euclid's data, in like manner corrected (1834)
Euclid, Euclid, Simson, Robert, 1687-1768 · Philadelphia : Desilver & Thomas · leaf 71
t, let F be the centrecause DE touches the circle ABC,and FC is drawn from the centreto the point of contact, FC is per-pendicular (18. 3.) to DE; there-fore FCE is a right angle; but ACEis also a right angle; therefore theangle FCE is equal to the angleACE, the less to the greater, whichis… … D C E Therefore if a PROP. XX. THEOR. The angle at the centre of a circle is double of theangle at the circumference, upon the same base, that is,upon the same part of the circumference.^ Let ABC be a circle, and BEC an angle at the centre, and BAGan angle at the circumference, which have the same…
Mathematics, Greek · Geometry · Trigonometry
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