Newcomb, Simon, 1835-1909 · New York, H. Holt and company · leaf 369
of the fifth tangent. Proof. Let the conic be projected into the circle whosecentre is 0, and let a, h, c and d be four points in whichthe fifth tangent intersects four fixed projected tangents,touching the circle at the points t^, t^, t^, t^.Because Angle aOb = i arc-angle tf^, j Angle bOc = i… … Therefore the anharmonio ratio of the pencil 0-abcd re-mains constant, being a function of the sines of constantangles. Therefore the anharmonic ratio of the row a, h, c, d re-mains constant (§296). Because this anharmonic ratio is constantly equal to thatof the corresponding points in the…
Geometry, Analytic
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