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Topic: Conic eccentricity through five points
Replies: 8   Last Post: Jul 22, 2013 2:08 PM

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Posts: 359
Registered: 9/16/06
Re: Conic eccentricity through five points
Posted: Jul 22, 2013 2:08 PM
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> what is the best invariant for a quadric surface?

> <
> ity_in_terms_of_...

Actually I was investigating curves of constant cross-ratio, an important invariant in projective geometry which turned out to be a conic :

(Conjecturing constant cross-ratio loci of a pencil in E2 )

So next question is to express cross-ratio of any conic in terms of A,B,C,D and E. Hope it will be interesting to find (calculate) it...

I for one think cross-ratio is the better invariant of a conic than eccentricity...Do you agree? Anyway, have fun!


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