Math CentralQuandaries & Queries


Question from ann, a parent:

what does planar curve mean in your definition of a cone?

Hi Ann,

A planar curve is one that lies in a plane. Some examples are

planar curves

To be the base of a cone the planar curve must be closed. In the plane, a closed curve is a curve with no endpoints and which completely encloses an area. (See Wolfram Mathworld.) Thus the line and parabola above can not be the base of a cone.

An example of a curve that is not planar is the curve formed by a coil spring.

coil spring


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