Go on eBay and buy the following Open University book sets. They go for around £30-50 a pop: MU123 (basics), MST124 (more complex). 6 months worth of study in each book set. If you like it do MST125 (even more complex) and M140 (stats) after. That's the first year of a mathematics degree literally from the ground up through GCSE and A-level stuff. If you really like it, get a student loan and do the associated accredited degree.
£30 for 6 months is pretty damn cheap and you get to keep it forever!
This is a proper accredited course developed over 50 years or so with its own textbooks and material from a respectable university, not a gamified subscription portal experiment put together by god knows who that can disappear in a puff of smoke at no notice.
I'm studying the Q31 (BSc Maths) on Open University.
I can second this recommendation. The maths books are _excellent_.
It's hard to explain how, but let me try: most of the maths textbooks I possess (plenty of them) are written with the assumption that you attend lectures at a classroom and use them for extra material/exercises/reference.
The OU books are written with the assumption that you learn from them as the primary material, so they go a lot further with regard to explaining things as well as producing them from first principles.
Yeah, MU123 is basic (high school) mathematics. The reason for that is that the way the Open University works, they have no formal requirements to join, so they cannot assume that students know even the basic stuff (because they might have left school earlier, or they might be out of formal education for years, or be from a different domain, etc), so the aim of that course is to quickly help you catchup regardless your background.
If you are above this level, you would start with the "intensive start", which skips MU123 (allowing you to pick another module in its place) and then starts with MST124 (precalculus, trigonometry and single-var calculus, roughly), moving you on to MST125 (intro to proofs, number theory, more calculus, linear algebra, etc), in a faster pace.
Yeah I get the part about filling in some missing foundation. But it's the level that surprised me. Some of the MU123 content is covered in 5th grade in the US, i.e. around age 10 or 11.
But I guess there are people who will have forgotten that stuff, if they're not using much math day to day.
£30 for 6 months is pretty damn cheap and you get to keep it forever!
ebay example of the latest edition for sale: https://www.ebay.co.uk/itm/197011707080
On archive.org too if you are happy with PDFs: https://archive.org/search?query=creator%3A%22The+MU123+Cour...
First MU123 book A: https://archive.org/details/BookAMU1232ndedOU2014/MU123-Book...
This is a proper accredited course developed over 50 years or so with its own textbooks and material from a respectable university, not a gamified subscription portal experiment put together by god knows who that can disappear in a puff of smoke at no notice.