Question 117665
If the lines through these 2 sets of points then their slope will be equal:
(6-3)/(11-2)=3/9=1/3
(21-18)/(8+3)=3/11
These slopes are not equal therefore the sides are not parallel.
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For these sides to be perpendicular their slopes must be negative recipricals of each other:
(6-3)/(11-2)=3/9=1/3
(18-3)/(-3-2)=15/-5=-3 
These 2 slopes are negative recipricals of each other therefore the sides are perpendicular.