1. Point A is the y-intercept of the line. You can adjust Point B to change the slope of the graph.
2. Create a new point that’s not on the graph. Create a line parallel to the red line that goes through this point.
3. Find the slope of both lines and write them on a piece of paper.
4. Push the refresh button in the upper-right corner of the coordinate grid. Change the slope and the y-intercept of the red line.
5. Create another point that is not on the line. Draw a line that is parallel to the red line and goes through this point. Write down the slope for both lines.
6. What do you notice about the slopes of parallel lines? Refresh the grid and try your prediction on a new line. Did it work?

7. Refresh the grid. Create a new point that is not on the line. Then, draw a line that goes through this point that is perpendicular to the line.
8. Write both slopes on a piece of paper.
9. Complete steps 7 and 8 again.
10. What do you notice about the slopes of perpendicular lines? Refresh the grid and try your prediction on a new line. Did it work?