1. Source: Discovering Geometry by Michael Serra

2.  Define a “good definition”  Identify counterexamples when possible  State converses of definitions  Define a right angle and an acute angle

5. A good definition...  is precise.  places an object to be defined into a class of well-defined similar things  is able to state how different an object is from the other members of the class.

6. STEPS: 1. Classify 2. Differentiate 3. Test

7. Let’s recall our SETS. Is this a well-defined set?  the set of famous songs of Michael Jackson released from 1980 – 1990  the set of numbers between -3 and 3

8.  Definition:  A polygon with exactly six sides is a hexagon. Re-state the definition… A hexagon is a polygon with exactly six sides.