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From: Bev Greco <email@example.com> To: Teacher2Teacher Public Discussion Date: 2008060412:30:27 Subject: postulate vs theorem for corresponding angles We are choosing a new text for our NYS Geometry course, and different texts present 2 column proofs differently. In our math department, there is a disagreement as to whether we can use the corresponding angles formed when 2 parallel lines are cut by a transversal as a postulate rather than a theorem. I can find it both ways in many places. We have always proven it as a theorem using an indirect proof. If we are to talk about true Euclidean proofs, is it incorrect to use corresponding angles as a postulate rather than a theorem? Some teachers feel it is not obvious that corresponding angles formed when 2 parallel lines are cut by a transversal are congruent. Others just feel that it is not acceptable under the title "Euclidean". Any ideas?
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