Ball, W. W. Rouse (Walter William Rouse), 1850-1925 · London, Macmillan · leaf 334
red to prove that AB and CD areparallel. If possible let them not be parallel, then they willmeet when produced say at M (or N). But the angle AFGis the supplement of BFG and is therefore equal to FGD.Similarly the angle FGG is equal to BFG. Hence the sumof the angles AFG and FGG is equal to two… … Conversely, if AB and CD be parallel, then ^^and CG arenot less parallel than FB and GD; and therefore whatever bethe sum of the angles AFG and FGC, such also must be the * Procius, ed. G. Friedleiu, Leipzig, 1873, pp. C62—368. 314! THE PARALLEL POSTULATE [CH. XIII sum of the angles FGD and BFG.…
Geometry · Cryptography · Ciphers
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