Where can I find Brief notes for first and second order?

Oct 2015
Does anyone have a link or any notes willing to share?

I need to refresh my memory on solving 1st-degree equations 2nd with constant coefficients and 2nd with variant coefficients.

I'm actually re-reading differentials equations and I believe I'm wasting time since I've already learned them and I have so many other courses to prepare for... I just don't remember all the techniques.