How do you determine if line pairs on a graph are perpendicular or parallel?Lines k, l, m and n have slopes of 2/3, -4, -1 1/2 and 1/4 respectively. Which pairs of lines are perpendicular?

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Both pairs of lines are parallel: Line m is the negative reciprocal of k, and line l is the negative reciprocal of line n. Therefore, lines m and k are perpendicular and lines l and n are perpendicular. Thats the rule: a pair lines, with one slope as the negative reciprocal of the other, are perpendicular. Good luck! 

two lines are parallel if they have the same slope.  two lines are perpendicular if they have opposite sign reciprocals.  1/4 and -4 are perpendicular.  none of the slopes are parallel.