I am having a hard time trying to understand this transformation from lorentz: https://imgur.com/a/WYWMO (You should ignore the spanish part and just focus on the math). I can’t understand well why they turn into what you can see in the second picture, when taking really small values of x. Also, I tried to aproximate to the fourth equation, but I get minus partial derivative of tau respect of x prime, instead of plus. I would appreciate your help, thanks. I hope this is understandable, it is my first post, and I have no knoweldge of latex.