How do you find perpendicular slope is it: Y sub 1 minus Y sub 2 divided by X sub 1 minus X sub 2.?
Best
Say you have two coordinates $\displaystyle (x_1,y_1)$ and $\displaystyle (x_2,y_2)$.
The slope is simply: $\displaystyle \frac{y_2-y_1}{x_2-x_1}$
Perpendicular slope, and the tangent normal to this point is the opposite reciprocal of that slope: $\displaystyle \frac{x_1-x_2}{y_2-y_1}$