why would it be inappropriate to dimension to a feature on a surface that is not perpendicular to the line of sight?

If you are drawing and dimensioning with a computer program the dimension will be inaccurate... If it is mechanical drawing then the fabricator would not have enough information to accurately measure the component. ie a circle turned a few degrees away from perp. would appear to be an ellipse. and may actually dimension that way

your supposed to flip the sign for the less than or greater than sighs when dividing by a negative.

Step-by-step explanation:

-4x←20

x→-5