where "θ" is the angle between a and b in the plane containing them (hence, it is between 0° and 180°), ‖a‖ and ‖b‖ are the magnitudes of vectors a and b, and n is a unit vector perpendicular to the plane containing a and b, in the direction given by the right-hand rule (illustrated). If the vectors a and b are parallel (i.e., the angle "θ" between them is either 0° or 180°), by the above formula, the cross product of a and b is the zero vector 0.