Teacher2Teacher 
Q&A #131 
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From: Susan Braford <s.braford@erols.com> To: Teacher2Teacher Public Discussion Date: 1998072810:22:44 Subject: Geometryideas for teaching proofs Have the students learn all theorems in if/then form, and definitions in if and only if (reversible). These can then be written on index cards that are divided in half down the middle with the "if" on the left and a single arrow pointing to the "then" on the right. Definitions have a double arrow because they are reversible. Now the student can "build" a proof just the way one would play dominoes, beginning with a given statement from the problem and concluding with the "then" part of the problem. You can model this by completing a simple proof with the students pulling out all the "cards" that have the given on the "if" (left half) part or the conclusion on the "then" (right half) part. Now the students have to build the bridge connecting the given and prove using additional cards just as you would in dominoes by connecting two cards, matching the right side of one with the left side of the next. Try it yourself first and let me know how it goes.
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