Answer:
-6/7
Step-by-step explanation:
The slope of DE is ...
(change in y)/(change in x) = (y2 -y1)/(x2 -x1) = (-3-4)/(1-7) = -7/-6 = 7/6
The slope of the line perpendicular to DE is the negative reciprocal of this:
perpendicular slope = -1/slope = -1/(7/6) = -6/7
___
