# Right-hand rule

From Knowino

The **right-hand rule** is a rule that appears in the cross product,

The direction of the unit vector **e**_{z} given as the cross product of unit vectors along the *x*- and *y*-axis is given by the right-hand rule, see photograph.

The case depicted here has a right (90° degree) angle α between the *x*- and the *y*-axis. However, the rule works for *any* angle α between *x*- and *y*-axis, as long as 0° < α < 180°. The *z*-axis is always perpendicular to the plane containing the *x*- and *y*-axes. If the angle α equals 0° or 180°, the cross product is the zero vector, which has an undetermined direction.