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 168
draw (31. 1.) GH paral-lel to BC: and.because BC is atright angles to ED and DA: BC isat right angles (4. 11.) to the planepassing through ED, DA. AndGH is parallel to BC; but, if twostraight lines be parallel, one ofwhich is at right angles to a plane,the other shall be at right (8. 11.) angles to… … 166 THE ELEMENTS OF EUCLID. BOOK XI. DA, meets it: therefore GH is perpendicular to AF; and conse-quently AF is perpendicular to GH, and AF is perpendicular toDE: therefore AF is perpendicular to each of the straight linesGH, DE. But if a straight line stands at right angles to each oftwo straight…
Mathematics, Greek · Geometry · Trigonometry
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