Question 40070
Floor plans for a building have the four corners of a room located at the points (2,3), (11,6), (-3,18) and (8,21). determine whether the side through the point (2,3) and (11,6) is perpendicular to the side through the point(2,3) and (-3,18).

The slope through (2,3) (11,6) is [6-3]/[11-2]=1/3
The slope through (2,3) (-3,18) is [18-3]/[-3-2]= 15/-5=-3

Since one is the negative reciprocal of the other the lines
are perpendicular.
Cheers,
Stan H.