…and I went there, kept scaling Mount Geek, picking up Oppenheim/Schafer’s “Discrete-Time Signal Processing” and two refresher/cheat books on Diff Eq and Fourier/Laplace/Hilbert transforms.
And now get to explain to my wife why I need $300 in textbooks. “Um… I flunked this in college?” - probably won’t cut it.
It’s by far the best option but I have to get kindle copies - already got rid of all my hardback textbooks. Some were kind of painful (I’d owned “Numerical Recipes In C” for like 30 years )