For lines to be parallel, the slopes have to be the SAME.
For lines to be perpendicular, the slopes have to be the exact opposite. (opposite sign and number)
For example(perpendicular):
slope is 2
the perpendicular slope is -1/2
slope is -4/5
the perpendicular slope is 5/4
12. line a and b are perpendicular
13. Line a: y = 3/5x + 1
Line b: y = 3/5x - 2/5
Line c: y = 4/6 + 5/3x
line a and b are parallel
14. Line a: y = 3x + 6
Line b: y = 6 - 3x
Line c: y = 2/3x + 6
Neither, none of them are parallel or perpendicular
15. Line a: y = -2/3 + 4/3x
Line b: y = -1/4 - 3/4x
Line c: y = 5 + 3/4x
line a and b are perpendicular
