Question 53824
determine whether the side through the points (2,3) and (11,6) is perpendicular to the side through the points (2,3) and (-3,18). 
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Slope #1 = [6-3]/[11-2]= 3/9=1/3
Slope #2 = [18-3]/[-3-2]=15/-5 =-3
Since each is the negative reciprocal of the other the lines are
perpendicular.
Cheers,
Stan H.