Reddit mentions of Mathematical Methods for Scientists and Engineers

If you're genuinely interested in learning quantum physics, the first thing I would start off with is learning multivariable calculus and differential equations. You can find lots of resources online, and it is absolutely crucial to have a solid background in math before you begin studying physics.

So following that, I would just learn basic physics using the calculus that you've learned. You can also find these resources online-- a detailed high school physics text using calculus will be more than enough to give you a background on kinetics and electricity and magnetism. This is to provide you with a solid background in physics, which will benefit you moving forwards. Along that vein, I would then read a textbook about "math methods for science and engineering," something like this. It will teach you several advanced math methods, but will avoid the sort of theoretical math that you will not need for an understanding of quantum physics.

After that, I would go through and gain a good foundation in modern physics. This will give you an introduction to the special theory of relativity, wave-particle duality, a very basic overview of quantum mechanics, and things like Schrodinger's equation and atomic models.

After that, I would take a deep dive into classical mechanics, which means you'll need to pick up an advanced text. Taylor's Classical Mechanics is a solid choice.

After that, I think you will be well equipped to tackle advanced quantum mechanics, and you can find excellent texts for that as well. I'd recommend Intro to Quantum Mechanics by Griffiths.

tl;dr-- I know this might be a bit overwhelming, but the basics of it is

1. Learn multivariable calculus
   
   
2. Learn differential equations.