Lewis Carroll's Curve

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This Demonstration shows a curve first defined by Lewis Carroll.

Contributed by: Izidor Hafner (August 2013)
Open content licensed under CC BY-NC-SA



In [1, p. 16], Lewis Carroll posed the following problem:

"If a regular tetrahedron be placed, with one vertex downwards, in a socket which exactly fits it, and be turned round its vertical axis, through an angle of , raising it only so much as necessary, until it again fits the socket: find the locus of one of the revolting vertices."

The answer and solution are given [1, p. 26, p. 100]. The equations for the locus are ; , where the tetrahedron has edge length 1, altitude , and .


[1] L. Carroll, The Mathematical Recreations of Lewis Carroll: Pillow Problems and a Tangled Tale, 4th ed., New York: Dover, 1958.

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