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Physical meaning of directrix?

  1. Sep 13, 2009 #1
    I suddenly realized that the very notion of a directrix seems odd to me.

    (1) I don't know any physical significance of such a thing

    (2) How anyone came to define the parabola as such

    Any help? I read some older posts about the history of the directrix/focus definitions of the conic sections and I can see the idea of unifying the conics through the ratio of distances from a point to the focus and from the point to the directrix but perhaps there is something more, something deeper, something physical?


  2. jcsd
  3. Sep 13, 2009 #2


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    Last edited by a moderator: Apr 24, 2017
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