# condition of parallel and perpendicular lines

- Author:
- Mathguru

- Topic:
- Straight Lines

We now see two perpendicular lines.
We can change the slope of of the lines by using a slider.
Enter the slope of the second line by entering the slope in the format “m= value” in the input line. For example, type m = 1/3 and press enter to get the line with slope 1/3.

Questions to think about
1. How can we calculate the second slope so that the two lines stay perpendicular?
2. If the product of the slopes is -1, then the two lines are ______?