1. 3-3 Slopes of Lines Objectives: To find the slopes of lines.
To use slopes to identify parallel and perpendicular lines.

2. Vocabulary
Slope
If and only if

3. Slope
In a coordinate plane, the slope of a line is the ratio of its vertical rise over its horizontal run.

4. Example 1

5. Example 1 cont.

6. Postulate 3-2
Two non-vertical lines have the same slope if and only if they are parallel.

7. Postulate 3-3
Two non-vertical lines are perpendicular if and only if the product of their slopes is -1.
Hint: opposite reciprocals

8. If And Only If
If both a conditional and its converse are true, it can be written in if and only if form.

9. Example 2

10. Example 3

11. Homework
3-3 Worksheet