1. Section 2-2 (cont.) Definitions

2. Definition Activity
Work with your surrounding classmates and write the definition for a “Polyglob.”

3. Good Definitions
A good definition uses clearly understood terms. The terms should be commonly understood or already defined.
A good definition is precise. Good definitions avoid words such as large, sort of, and almost.
A good definition is reversible. That means that you can write a good definition as a true biconditional.

4. Example (Me)
Show that this definition of perpendicular lines is reversible. Then write it as a true biconditional.
Definition: Perpendicular lines are two line that intersect to form right angles.
Conditional: If two lines are perpendicular, then they intersect to form right angles.
Converse: If two lines intersect to form right angles, then they are perpendicular.
Biconditional: Two lines are perpendicular if and only if they intersect to form right angles.

5. Example (We) Definition: An airplane is a vehicle that flies.
Conditional:
Converse:
If it is an airplane, it is a vehicle that flies.
True
If it is a vehicle that flies, then it is an airplane.
False – counterexample: helicopter

6. Example (You)
Definition: A right angle is an angle whose measure is 90.
Conditional:
Converse:
Biconditional:

7. Homework: Section 2-2 p.90 #’s 18-23, 33-37