vectors. always rmb point to point. just the start and ending point are important. Travel from A to C. I need to travel from A to B, then from B to C. Direction is very important, so you define a direction as positive and you move in that direction, its considered positive. However, if you move in the opposite direction, it will be negative. Part C use Pythagoras's theorem, a standard way to prove for right angle triangles. Tutor Ong