Young, George, jr, Baxter, Hubert Eugene, joint author · New York, The Macmillan Co. · leaf 178
curve called a VIII, § 145] CURVED SURFACES 161 conic section. If the inclination of the cutting plane is equalto that of the cone, the curve will be a parabola. (See Fig.156 o, and compare with § 112.) In the figure, the plane Pbeing parallel to the element ab, it is readily seen that the… … Fig. 157 than that of the cone the curve is an hyperbola. (See Fig. 156 cand § 112.) From the figures it is easy to see that the ellipse is a closedcurve, symmetrical about two axes, and that the hyperbola isan open curve of two equal branches. Projections. The envelope (§ 142) of a cone consistsof…
Geometry, Descriptive
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