I took three years worth of analytical geometry, linear algebra, trig, calculus, etc in college. Forty years, later I have retained just enough to realize how much I don't remember. I am currently working my way through Kline's Calculus: An Intuitive and Physical Approach, taking notes and doing the problem. I am backfilling on what's called pre-calculus these days whenever I hit some concept or formula that I don't remember, which is most often in geometry or trig.
Why you ask? Can't really grok Maxwell's equations or general relativity, without them.
Make sure that backfill includes tensor algebra and Riemannian geometry; the authoritative book is tough going without some working knowledge of both (not joking; I'm still working my way though it and while it's quite a good source it does get deep at times) :
Tensor algebra and Riemann geometry will be new territory for me. At my current pace, I figure tackling relativity is at least two years out. Maxwell's equations are, by comparison, easier sledding.
Yes, if you know differential equations, Maxwell can be deciphered fairly well. We actually had a physics professor write them down in integral form as a "4 equations in 4 unknowns" set and proceed to solve for the wave velocity. Not surprisingly, the result, once you plugged in the magnetic and electric constants of free space, came out to be "c". It was eye-opening to see that all of EM theory proceeds from a compact set of equations.
The main issue in GR is that you have 10
nonlinear differential equations to solve (meaning the inputs depend on the outputs). This necessitates that you make some assumptions about the form of the solution and is what led to Einstein's long search for a compatible metric so that he could express his requirements consistently. Riemannian (differential) geometry turned out to be the key, as it divested itself of the coordinate restrictions we typically assume in our customary Cartesian system. Pretty complex stuff, yet it has a beauty and elegance all its own.
I highly recommend John Wheeler's
A Journey Into Gravity and Spacetime from Scientific American. Written entirely without the complex math, it nonetheless captures the spirit of general relativity and is quite entertaining as well.