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which shows L as the directrix of the parabola: http://commons.wikimedia.org/wiki/Image:Parabola_with_focus_and_directrix.svg Date 13 December 2007 (original
*The distance to a focus, ''F'', from the centre ''C'', is the eccentricity, ''e'' multiplied by the semimajor axis, Uploaded with derivativeFX English