Got the answer from this site:

http://www.nfostergames.com/Lessons/VectorMath.htmVector subtraction is as easy as simple arithmatic. You simply subtract each component of one vector from the other.

c = a - b

Example:

Vector a = (3, -5, 7)

Vector b = (5, -2, -9)

Vector c = (3 - 5, -5 - -2, 7 - -9) = ( -2, -3, 16)

So, what does vector subtraction get us? A couple of useful things. It gives us the direction from one vector to another. In this example, 'c' is a vector that points from the point represented by vector 'b' to vector 'a'. Using vector 'c' we can determine a direction and distance from b to a, which we shall show in the next two examples.

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