condition of parallel and perpendicular 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 ______?