Smart, Edward Howard · London : Macmillian and Co. · leaf 242
, and theorem (a) is proved forthe circle. Projecting and applying the same argument as in §1, itholds likewise for the conic. 214 PROJECTIVE GEOMETRY To prove (6), let a, b, c, d, v be tangents to the conic atA, B, C, D, V respectively, the first four being fixed in eachcase, and V and v variable… … Pig. 107&. Then v{abcd} denoting as usual the cross-ratio of the rangedetermined by a, b, c, d on v, is, by § 1, equal to that of thepencil formed by the polars of va, vb, vc, vd, i.e. VjABCD}. But the latter is constant by theorem (a). .. theorem (b) is proved. §3. Deductions from these…
Geometry, Projective
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