condition of parallel and perpendicular lines

We now see two perpendicular lines. We can move the lines by clicking and moving points A or B. The lines will stay perpendicular.
Questions to think about 1. What do we observe about the slopes of the two lines? 2. Multiply the slopes together using a calculator. What do we get? Take approximate value. 3. If one of the lines is horizontal, then the other line is _________? 4. If one slope is 0, what is the other slope?