Use the interactive points below to draw lines & display their slope

Just drag any point and you will see that line's graph and slope change accordingly. The interactive exercise below will tell you when you've made the lines parallel or perpendicular--
whenever that happens, examine the slope of both lines. Whenever the lines are parallel, determine what special relationship exists between the slope of parallel lines. Likewise, try to determine the spcial relationship of the slope of lines that are perpendicular.