^Linear momentum conservation
will be a constant , in other words the linear momentum of a system is constant in time if net external force acting on it is zero. LCLM is equivalent to NTL. Consider a two particle system. Let the total linear momentum of the system is not changing with the time i.e.
i.e., the two forces i.e. action & reaction are equal & opposite. i.e. for a two particle system the linear momentum of a system will not change with the time only if forces acting on the system are equal & opposite so that net force on the system is zero.
This justifies that LCLM is equivalent to NTL.