Young, George, jr, Baxter, Hubert Eugene, joint author · New York, The Macmillan Co. · leaf 175
drawingprojections, to keep the visible and the invisible portions clearlyseparated in the mind. 158 DESCRIPTIVE GEOMETRY [VIII, § 143 143. Ruled Surfaces. Ruled surfaces vary widely in char-acter. Since all ruled surfaces have the same generatrix (§ 140),this variation must be the result of the… … Lower nappe
Geometry, Descriptive
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