Coba jelasin is the magnetic constant, dari Médan magnétik dalam bahasa sunda dong

is the unit displacement vector from the wire element to the point at which the field is being computed, and

is the distance from the wire element to the point at which the field is being computed.

This is a consequence of Ampere's law, one of the four Maxwell's equations. Alternatively, it can be thought of as a true, empirical law in its own right, which contributes to the derivation of Maxwell's equations. From a practical point of view, though, the law is true and useful regardless of its philosophical origin.