Proving Particle Velocity Exceeds c in All Inertial Systems

[martyf]

Homework Statement

Show that if an hypothetical particle has v>c in a inertial system , v>c in any other
inertial system

Homework Equations

The Attempt at a Solution

 

[dx]

Take a space-like four-velocity and apply a Lorentz transformation to it. Then show that the result is also space-like.

 

[martyf]

Ok, thanks!