On Fri, 16 Jun 2000, Paul Yiu wrote [edited]:
> Let P be a fixed point, and L a given line with tripole L*.
> Then P/L is the conic through the traces of P and L*.
It seems to me that "the conic through the traces of P and Q"
deserves a name! Let's call it [P,Q] for the moment, so that
your theorem asserts that P/Q* = [P,Q], which is symmetric in
P and Q, so you've proved that P/Q* = Q/P* - wonderful!
This has, I think, some notational consequences. It's natural to
use 1/P for the tripolar, in view of the coordinate form:
tripolar of the point (X:Y:Z) is the line (1/X:1/Y:1/Z|).
In this notation, your result becomes
P/(1/Q) = Q/(1/P) is a symmetric "product" [P,Q]
which might almost be expected! I wonder if there's any more
"algebra" of this type?
> Let P be a fixed point. Then P/P* is the inscribed conic with
> Brianchon point P. The center of the conic is the inferior of the
> isotomic conjugate of P.
I think your "Brianchon point" of an inconic is the same as my
"perspector" of it? I used to use various names for these notable
invariant points of inconics and circumconics until I noticed only
last year the important fact that ABC is in perspective with its
dual triangle with respect to ANY conic, not just in- and circum- ones,
and so switched to the term "perspector" for all cases.
Regards, John Conway