## Quick Idea from #TMC13

August 4, 2013I just thought of this as I was reading some recaps of TMC13: During “My Favorites”, Chris Lusto offered the idea of having students work out the definition of a circle.

What just struck me was one of the activities challenged the students to come up with an example that fit a classmate’s definition but was **not** a circle. COUNTEREXAMPLE!! Counterexamples (especially **geometric** counterexamples) are so tricky for students to get. Here’s a built-in example of why they’re a big deal. Love!

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