An elementary treatise on modern pure geometry (1893)
Lachlan, Robert · London, New York, Macmillan and Co. · leaf 109
f a tetragram. See § 142, Ex. 2. Ex. 6. If ahcd be any tetragram, and if the line joining the points ah, cdintersect the line joining the points ad, he in the point 0; show that the linesdrawn through 0 parallel to the lines a, h, c, d will meet the lines c, d, a, hrespectively in four collinear… … Let A, A; B, B; C, G\ be the three pairs of opposite verticesof the tetragram. Then evidently A and A are a pair of centresof the tetrastigm BC, BC. Hence, by § 141, it follows that BB,and GC, cut AA in two points which are harmonic conjugateswith respect to A and A. If the lines of the tetragram…
Geometry
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