Smart, Edward Howard · London : Macmillian and Co. · leaf 235
ils are in perspective ? § 6. Prop. Projective ranges and pencils are homographic,and conversely. For evidently the cross-ratio of any four elements is equalto that of the corresponding four in the projective form. The converse is true, for referring to Figs. 105a and h, eachrange (or pencil) is in… … Pio. 106. points on the two ranges as we please, given the liomographieaxis and a pair of corresponding points. For if P, P be such 208 PROJECTIVE GEOMETRY a pair, the point Q corresponding to Q is obtained by joiningP to the point where PQ intersects the axis, and producingthis line to cut the…
Geometry, Projective
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