9: Perpendicular VS Parallel Slopes and their Equations
Video: https://www.youtube.com/watch?v=hQ64ZoDvN_k
More: http://www.shmoop.com/video/slopes-of-parallel-and-perpendicular-lines
It's NEGATIVE Reciprocal (Opposite Upside Down 2 will be -1/2 or - 5/4 will be 4/5 )
Parallel Notes: http://www.coolmath.com/algebra/08-lines/13-parallel-lines-01
Perpendicular Notes: http://www.coolmath.com/algebra/08-lines/14-perpendicular-lines-01