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How is this 90 degrees?

  1. Feb 6, 2007 #1
    http://www.e-xamit.ie/2005test/php/GetDocByID.php?id=562&prep=565&soln=562&tip=570&port=566 [Broken]

    I can't figure out how it takes the angle dec to be 90 degrees? How?
    Last edited by a moderator: May 2, 2017
  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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