Elements of geometry : containing the first six books of Euclid, with a supplement on the quadrature of the circle, and the geometry of solids : to which are added, Elements of plane and spherical geometry (1826)
Playfair, John, 1748-1819, Euclid · Philadelphia : Marot & Walter · leaf 293
writer wlio appears to have attempted todo this, is Ptolemy the astronomer, who wrote a treatise expressly onthe sulsject of Parallel Lisies. Proclus has preserved some accountof this work iu the Fourth Book of his commentaries: and it is curi-ous to ohserve in it an ars^ument founded on the… … be equal to two rii^ht angles, Ptolemy reasons thus: If the anglesAGH, CHG be not equal to two right angles, let them, if possible, begreater than two right angles; then, because the lines AG and CHare not more parallel than the lines BG and DH, the angles BGH,DHG are also greater than two right…
Euclid's Elements · Geometry · Trigonometry
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