The first six books of the elements of Euclid, in which coloured diagrams and symbols are used instead of letters for the greater ease of learners (1847)
Byrne, Oliver, Whittingham, Charles, 1795-1876, Chiswick Press · London : William Pickering · leaf 27
BOOK I. ELUCIDATIONS. xxv the letter which marked the vertex of the angle beingalways placed in the middle. Thus the black and red linesmeeting together at C, form the blue angle, and has beenufually denominated the angle FCD or DCF The linesFC and CD are the legs of the angle; the point C is…
Euclid's Elements · Geometry
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