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An obtuse triangle and its circumcenter

  1. Sep 9, 2008 #1
    I'm having a bit of difficulty proving this, but this is what I have so far:

    Let a circle with a center O and a diameter AD. Let triangle ABC be a triangle with all points on the circle and angle A be greater than 90. Because of III. 20, and BOC is 2 times the size of angle A.

    This is all I can reason through. I can see that it works on GSP, but I haven't been able to create a synthetic proof.
  2. jcsd
  3. Sep 9, 2008 #2


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    Staff: Mentor

    Could be my English fails me, but I have no idea what you are trying to prove.
  4. Sep 9, 2008 #3
    I'm trying to prove that the circumcenter of an obtuse triangle lies outside of the triangle.
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