Direction of two points

Question

Some high school math concept has been forgotten, so I ask here.

If I have two points p1(x1,y1), p2(x2,y2), the direction is P1-->p2<

Answer 1

A nice way to remember which way the subtraction goes is to think of what the vector actually does. Imagine vector v resting at p1, pointing and connecting to p2. This means that p1 + v = p2. Therefore, v = p2-p1.