Hi people, Thanks to use your time in me! I saw and understood the maths to arrive to this: Where primed fields are the electromagnetics fields saw in a system S´in movement respect another system S with velocity in X axe thats coincides with X´s axe. My question is about a thing that bother me that is the assimetry I saw in Zs and Ys components with a plus in one and a minus in the other instead of minus or plus in both. I can´t understand the physical reason behind. Thanks!