We're starting geometric proofs now, and yesterday we did two activities to prep for this. First, I wanted the students to be familiar with some basic definitions and to know that they are biconditionals, and see how they're used as reasons for proofs. Second, I wanted the students to look at partial pieces of proofs and fill in the blanks with reasons, or steps if given the reasons.
Here's an activity I did to get them thinking about adjacent angles, linear pairs of angles, and vertical angles:
We first looked at the definition of adjacent angles. Then I had them go down that column and either indicate YES, or if NO, then list the parts of the definition it violated. Then we did the same with linear pair. Then I just had them write on the LHS which one(s) were vertical angles.
Next we took notes on how theorems, definitions, postulates, properties could be used as proof reasons, and I had them refer to a print out of our basic ones so far (along with definitions), and do the following:
The pesky bell rang, and we ran out of time, so I'll have to see how they did next class.