Counterexamples

We're moseying along in geometry and are now doing truth tables and "Laws of Inference". Soon we'll be taking it to one step proofs and then real proofs. Before we get there, though, I want the kids to start thinking about what proves and what disproves things. Is it enough to consider EVERY EXAMPLE IN THE WORLD and if they're all true, then the statement is true? If you just find one counterexample to a statement does THAT make it a false statement (what if you find an example that makes it true?)?

Anyway, along those lines, I made up the following sheet:





I love the document camera because we worked on the 1st few one at a time, and then I could put various students' papers up there and we discussed if their drawings were suitable or not and how to fix them if they weren't.