Question on §3 of Einstein's 1905 paper

[Brett Oertel]

Hi guys,

This is my first time posting on PF!

I have a question on §3 of Einstein's paper "On the electrodynamics of moving bodies."My problem is with the following mathematical statements:

Hence, if x' is chosen to be infinitesimally small,

or

I have just finished high school, and whilst I have finished two other books which concerned Special Relativity (and understood them well) I think I do not know enough maths to understand what i pasted above. Could someone explain how he gets from step 1 to step 2 please?
Or, perhaps could someone tell me what topics in calculus I must learn in order to understand it myself?

Thanks!

EDIT: I found many other threads asking the exact same thing as me... Oops! I managed to derive it on my own so no answer is necessary :).

 

[Drakkith]

Oops! I managed to derive it on my own so no answer is necessary :).

Mind posting the derivation so others can see how it was done?