Plane and solid geometry . nd lowernappes of a conical these out in the figure. The student should observethat by changing the directrixfrom a broken line to a curvedline, a pyramidal surface becomes a conical surface. 839. Def. A cone is a solid closed figurewhose boundary consists of the portion of aconical surface extending from its vertex toa plane cutting all its elements, and thesection formed by this plane. 840. Defs. By referring to §§ 748 and822, the student may give the definitionsof vertex, base, lateral surface, and elementof a cone. Point these out in the figure. 841
Plane and solid geometry . nd lowernappes of a conical these out in the figure. The student should observethat by changing the directrixfrom a broken line to a curvedline, a pyramidal surface becomes a conical surface. 839. Def. A cone is a solid closed figurewhose boundary consists of the portion of aconical surface extending from its vertex toa plane cutting all its elements, and thesection formed by this plane. 840. Defs. By referring to §§ 748 and822, the student may give the definitionsof vertex, base, lateral surface, and elementof a cone. Point these out in the figure. 841. Def. A circular cone is a cone containing a circularsection such that a line joining the vertex of the cone to thecenter of the section is perpendicular to the section. Thus in Fig. 4, if section AB oi cone V-CD is a O with center0, such that VO is _L the section, cone V-CD is a circular cone. 842. Def. The altitude of a cone is the perpendicular fromits vertex to the plane of its base, as VC in Fig. 3 and VO iuFig. FiG. 2. Cone BOOK VIII 389 843. Defs. In a cone with a circular base, if the line join-ing its vertex to the center of its base is perpendicular to the V
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectgeometr, bookyear1912
