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Frustum of: Top and base are parallel to each other (Fig. 6.19).

Figure 6.19

6.4 POINTS ON THE SURFACES

The point lies on a surface if lies on a line lying on this surface (Fig. 6.20, 6.21, 6.22).
It is well to remind that if any prism, pyramid, cylinder, or cone is cut by a plane parallel to
the base, the intersection is always a figure like the base in shape, and parallel to it in position.
It is well also to remind that if any surface of revolution is cut by a plane perpendicular to the
axis, the intersection is always a circle.
Auxiliary intersection is parallel and congruent to the base. It is often used for surface point
finding (Fig. 6.22). Generator method is used for surface point finding too (Fig. 6.21).

Figure 6.20 Figure 6.21

Figure 6.22

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