Making Parallel and Perpendicular Lines with sliders
Below are 2 lines made using the generic y=mx+b using sliders. Play with the sliders to see when the two lines are parallel (when they don't intersect ever) and when they are perpendicular (when they intersect at 90 degrees). The lines will be parallel when they have the same slope, but their y-intercepts can be different. The lines will be perpendicular when their slopes are negative reciprocals, and again the y-intercepts can be different.