I A ai bj ck= + + . How would you write a vector that is parallel to the x-or i direction? Referring to Figure 2.2,
I Apoints in the
x-direction if b = c = 0, so I A ai= . Now, how would you write a vector that points in the x-direction and has
a magnitude of 1 unit? Clearly, a = 1, so I A i= . Hence, i is itself a vector with a magnitude of one unit point-
ing in the positive x-direction; it is appropriately called a unit vector. Likewise, jand k are unit vectors pointing in the positive y-and z-directions.