Question 42110
The slopes are perpendicular if their slopes are negative reciprocals of each other.
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For example: m1 is perpendicular to m2 because m1 = 2/1 and m2 = -(1/2). 
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First, find the slope of each set of coordinate points. 
The formula for slope is:
delta y/delta x = (y1-y2)/(x1-x2):
The slope m1 of (2,3) and (11,6) = (3-6)/(2-11) = -3/-9 = 1/3
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The slope of m2 of (2,3) and (-3,18) = (3-18)/2-(-3)= -15/5 = -3/1
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The slopes are the negative reciprocals of each other:
1/3 is the negative reciprocal of -3/1.
Therefore, the lines are perpendicular.