# Investigating Slopes of Parallel and Perpendicular Lines

- Author:
- Lydia East

## Parallel and Perpendicular Lines

Write each question and answer it on your own paper to find a relationship between the slopes of parallel lines and the slopes of perpendicular lines.

1. Name each line in the picture.
Black:
Red:
Purple:
2. Which lines are parallel? What are their slopes?
3. Which lines are perpendicular? What are their slopes?
4. Now, drag point A until the slope of the black line is 3.
5. What is the slope of the red line now?
6. What is the slope of the purple line now?
7. Make a conjecture (prediction) about the slopes of parallel lines.
8. Make a conjecture about the slopes of perpendicular lines.

**Further Investigation**Can parallel lines have the same y-intercept? Explain why or why not. Can perpendicular lines have the same y-intercept? Explain why or why not.