An elementary treatise on modern pure geometry (1893)
Lachlan, Robert · London, New York, Macmillan and Co. · leaf 112
yz Y X Therefore by § 105, since the points X, Y, Z are collinear, so also arethe points J, Y\ Z. If we take the line at infinity instead of the line XYZ, the points X, Y,Z become respectively the middle points of AAI, BB, CC and thus we havethe theorem of § 151. 154. The lines connecting any point… … 96 INVOLUTION PROPERTY OF A TETRAGRAM. Let A, A; B, B; G, C; be the pairs of opposite vertices of atetragram, and let 0 be any point. Then the pencil 0 [AA, BB, CC}will be in involution. Since ABC is a transversal of the triangle ABC, we have BA CB AC _CA-AB-BC~ Hence as in § 109, Ex. 2, sinSO^ sin…
Geometry
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