Finding the resultant vector (A - B) is equivalent to finding a vector C which will satisfy the equation C = A - B or C + B = A. The latter equation makes it possible for us to use the knowledge of adding two vectors to find the rule on vector subtraction.

When we place the tails of vectors A and B together, we see that vector C drawn from the head of vector B to the head of vector A will satisfy the equation B + C = A. Therefore, vector C is the resultant vector of A - B. The general rule is that the vector drawn from the head of the second vector to the head of the first vector will give the vector difference.