Newcomb, Simon, 1835-1909 · New York, H. Holt and company · leaf 363
and let a, h, c and dbe the points in which it intersectsthe plane of projection. Because the lines of the pencilmust all lie in one plane, thepoints a, h, c and d will lie in astraight line. If 0 be the projection of 0, the projected pencil will beO-ahcd. Then the anharmonic ratios of each pencil… … 334 MODERN GEOMETRY. Harmonic Points and Pencils. 303. Def. When the anharmonic ratio of four points isnegative unity, tliey are called a row of four harmonicpoints, and each pair of conjugate points is said to dividethe segment joining the other pair harmonically. So a pencil of four lines of…
Geometry, Analytic
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