Hostname: page-component-cd9895bd7-p9bg8 Total loading time: 0 Render date: 2024-12-28T13:34:53.655Z Has data issue: false hasContentIssue false

The existence of sextactic points

Published online by Cambridge University Press:  24 October 2008

D. L. Fidal
Affiliation:
Department of Pure Mathematics, University of Liverpool

Extract

Let M be a plane oval (a smooth curve without inflexions). In this note we show that a generic such M (where the precise assumptions will be stated later) has to have at least one sextactic point, that is a point p where the unique conic touching M at p with at least 5-point contact actually has 6-point contact. This existence problem came into prominence whilst [2] was being written. It was hoped to use the existence of sextactic points to show that the Morse transition on a 1-parameter family of focoids with signature 0 or 2 could not occur. The problem proved to be remarkably stubborn, however. Indeed, the geometric interpretation of sextactic points as given in § 3 was totally unexpected.

Type
Research Article
Copyright
Copyright © Cambridge Philosophical Society 1984

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

[1]Bruce, J. W., Giblin, P. J. and Gibson, C. G.. On caustics of plane curves. Amer. Math. Monthly 88 (1981), 651667.CrossRefGoogle Scholar
[2]Fidal, D. L. and Giblin, P. J.. Generic 1-parameter families of caustics by reflexion in the plane. Math. Proc. Cambridge Philos. Soc. 96 (1984), 425432.CrossRefGoogle Scholar