Hey everyone. I consider myself a math enthusiast and I find high-rated math problems on this platform (+ more for example Atcoder or SPOJ) eye-catching (let's say around 2300 or above). That doesn't mean lower ones (like 2000-2200) are not interesting, but anyways, the main issue is I haven't learned much essential knowledge and I cannot apply those sometimes due to lack of practice.

Because of that, can anyone suggest me some documents about linear algebra that helps me understand the concepts better and also some problems (not necessarily cp-related) + some tips when I encounter those problems ?

Note: Anything else discussing about geometry also suits me quite a lot as I'm more of an algebra guy.