2. Writing Definitions First – Classify what it is Second – how does it differ from others in that classification EXAMPLE: – A Square is a __________ that ______________ – Classify itHow does it differ from others?

3. Counter Examples EXAMPLE – A square is a figure with four equal sides Is this good? If not, produce a counter example Counterexamples An example used to prove a statement false Sketch possible shapes that have the above qualities but is not a square

4. A Good Definition A square is a quadrilateral that is equiangular and equilateral – (a 4-sided polygon with equal angles and equal sides)

5. Beginning Steps to Creating a Good Definition Classify your term. What is it? What class/group does it fit into? Differentiate your term. How does it differ from others in that class/group? Test your definition by looking for counterexamples.

6. Define these terms Parallel Lines Perpendicular Lines Classify, differentiate, test each term Parallel lines are coplanar lines that do not intersect. Skew lines are non-coplanar lines that do not intersect Perpendicular lines are intersecting lines that form 90˚ angles.

8. Types of Angles Acute Angle: an angle that measures between 0° and 90° Right Angle: an angle that measures exactly 90° Obtuse Angle: an angle that measures between 90° and 180°

9. Angle Relationships Complementary Angles: Two angles whose sum of their degree measurements equals 90 degrees. Supplementary Angles: Two angles whose the sum of their degree measurements equals 180 degrees. 50˚ 130˚ 40˚ 50˚

10. Angle Relationships

11. Linear Pair of angles A linear pair of angles are two angles that are adjacent and supplementary angles. If two angles form a linear pair, then they are supplementary.

12. Vertical Pair of Angles Vertical angles are two angles that are created by two intersecting lines and are opposite each other. If two angles are vertical angles, then they are congruent. < 1 and <3 are a vertical pair of angles < 2 and <4 are a vertical pair of angles