Check out the attached image below. I've marked two red points on the line such that the points have whole number coordinates. This way I could compute the slope of this line to be -2/5
We move down 2 units (rise of -2) as shown by the blue arrows. Afterward, we move 5 units to the right as shown by the green arrows (which is the run). This gets us from the left red point to the right red point.
rise = -2, run = 5
slope = rise/run = -2/5
the original line shown has a slope of -2/5
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Next we do two things to get the perpendicular slope.
Flip the fraction: -2/5 becomes -5/2
Flip the sign: -5/2 becomes +5/2 or simply 5/2
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Final Answer: 5/2
