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 170
h passes through DE, EF, and let it meet that plane in G;and through G draw GH parallel (31. 1.) to ED, and GK paral-lel to EF; and because BG is perpendicular to the plane throughDE, EF, it shall make right an-gles with every straight line meet-ing it in that plane (3. def. 11.). BBut the straight… … See Note. 168 THE ELEMENTS OF EUCLID. BOOK XI. plane with it) the angles GBA, BGH are together equal (29. 1.)to two right angles: and BGH is a right angle, therefore also GBAis a right angle, and GB perpendicular to BA^ for the same rea-son, GB is perpendicular to BC: since therefore the straight…
Mathematics, Greek · Geometry · Trigonometry
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