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 299
the Jegments of the bafe, togetherwith the fquare of the Jlraight line whichbifedls the angle. Let be drawn, making^ = ^; then fhall X + ^r \ defcribe I About y \ defcribe J (B. 4. pr. 5), produce 1 ■■ to meet the circle, and draw ■■■»>— Since ^ = ^^ (hyp-)and ^^ = ^ (B. 3. pr. 21), • * •C*i»l»l… … fhall Y from any angle of a triangle aJlraight line be drawn perpendi-cular to the bafe; the rectanglecontained by the fdes of the tri-angle is equal to the reSlangle contained bythe perpendicular and the diameter of thecircle defcribed about the triangle.
Euclid's Elements · Geometry
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