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 68
= A^ = t (pr. 29.) … and common to the two triangles. /. \
Euclid's Elements · Geometry
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