Plane Sections of a Cone of Revolution. 189 
P 
tan a 
of the cone will cut from the cone a section whose latus 
rectum is 2p. 
The following geometrical construction gives the value of 
k for any assumed value of p. 
Parallel to an element, CP, of the cone, (Figure 3), in 
from the vertex 
Any plane, therefore, at a distance 
FIGURE 3. 
the axial plane through this element, and at a distance from 
it equal to one-half the given latus rectum, OQ, draw a line 
MN. Through £, the intersection of MW with the axis, 
