We can also add B to A , Fig 2-4a, using the triangle rule, which is a special case of the parallelogram law, whereby vector B is added to vector A in a "head-to-tail" fashion,i.e., by connecting the head of A to the tail of B, Fig 2-4b. The resultant R extends form the tail of A to the head of B. In a similar manner, R can also be obtained by adding A to B. Fig 2-4c. By comparison,it is seen that vector addition is commutative ; in other words, the vector can be added in either order, i.e., R = A + B = B + A.