The first six books of the Elements of Euclid, in which coloured diagrams and symbols are used instead of letters .. (1847)
Euclid, Byrne, Oliver · London, W. Pickering · leaf 26
the mea-fure. The vertex of an angle is the pointwhere the fides or the legs of the anglemeet, as A.An angle is often defignated by a fingle letter when itslegs are the only lines which meet to-gether at its vertex. Thus the red andblue lines form the yellow angle, whichin other fyftems would be… … 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…
Geometry
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