Calculating vector ab from vector a and b.

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( Vector AB ) = ( Vector B ) – ( Vector A )

Think of this logically when you have the equation 10 – 2 you get 8 ( a positve value )
However if you do 2 – 10 you get the same magnitude 8 but opposite direction -8.

Use this to understand the vectors since the point of Vector AB is moving from A to B you want to know whether its moving in the positive of negative direction.

If B had a greater value of position than A then obviously it moved in the
positive direction to achieve that greater value and that is why B – A (larger – smaller ) has to be positive. If it had a lesser value than A then it moved in the negative direction and that is why the value of B – A would then be negative (smaller – larger).

And in reality you are subtraction the vectors OB – OA ( O being the point of origin ) so the difference between these to vectors is a displacement.

I really hope i was of any help to answer your question.

🙂