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How is this 90 degrees?

  1. Feb 6, 2007 #1
    Last edited by a moderator: Apr 22, 2017 at 3:37 PM
  2. jcsd
  3. Feb 6, 2007 #2


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    Line segment ce is parallell to line segment ab. Line segment ad is perpendicular to ab at a, hence, ad is perpindicular to ec at e.
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