Date: Jul 28, 2011 1:48 AM
Author: Rob Johnson
Subject: Re: Inverse of a conic with regard to the centre is an oval of Cassini

In article <>,
Ken Pledger <> wrote:
>In article <>, Rob Johnson <>

>> ....
>> If we invert the points (x -> x/r^2, y -> y/r^2) ....

>Then I rushed into writing

>> x -> (r^2)/x, y -> (r^2)/y ?

>Wrong. Of course he intended r^2 = x^2 + y^2. Sorry.

I'm sorry. This post did not have a References header so it was not
linked to the original thread in my newsreader. I replied in the
original thread before I saw this post.

Rob Johnson <>
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