I'm learning differential equations and waves - following online courses and reading some textbooks - and I find that quite often, the use of Phasors, equations combining sinusoidal waves of different amplitudes and frequencies (the derivation of beats)...etc...they're explained really briefly, without a lot of diving deeper into them, and then applied.
Is there a specific "math" which I could study, or textbook I could read, that presents these subjects more explicitly? The more geometric and intuitive the math book is, the better! I tried looking for "wave mathematics" but...found mostly really advanced books. Complex Analysis didn't seem to fit either.
All and any recommendations are welcome.
Edit:
Books on the differential equations of waves are helpful...but, that's not really what I meant. What I really want is something that starts simpler.
What led me to asking this question is that it took me a long time to understand the geometric intuition for how to combine waves of the same amplitude but different frequencies (for which this - https://www.jstor.org/stable/27965328?seq=1 - helped quite a bit) and I still don't understand at all how to combine them if they have different amplitudes!
Is there not anything simpler than a differential equations approach, or perhaps a book that DOES go into the differential equations, but also does so explaining each step, instead of skipping over the "basic" math of waves?
Thanks again.