Compass Equivalence Theorem - Construction

Construction

We are given points A, B, and C, and wish to construct a circle centered at A with the same radius as BC (the first green circle).

  • Draw a circle centered at A and passing through B and vice versa (the red circles). They will intersect at point D and form equilateral triangle ABD.
  • Extend DB past B and find the intersection of DB and the circle BC, labeled E.
  • Create a Circle centered at D and passing through E (the blue circle).
  • Extend DA past A and find the Intersection of the DA and the circle DE, labeled F.
  • Construct a circle centered at A and passing through F (the second green circle)
  • Because E is on the circle BC, BE=BC.
  • Because ADB is an equilateral triangle, DA=DB.
  • Because E and F are on a circle around D, DE=DF.
  • Therefore, AF=BE and AF=BC.

Read more about this topic:  Compass Equivalence Theorem

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