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 138
Af and ^^ . ^^1 and ^r of any quadrilateral figure in-fcribed in a circle, are together equal totwo right angles. Draw and … the diagonals; and becaufe angles in the fame fegment are equal ^W =: ^^and ^r rr: ^^ |add ^ to both. two right angles (B. i. pr. 32.). In like manner it maybe Ihown that, Q. E. D. io6 BOOK III. PROP. XXIII. THEOR.
Euclid's Elements · Geometry
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