What kind of 2D library? Graphics, or physics? or something else?
I like this book alot, it says collision detection, but it also has a lengthly intro to many of the concepts of simulated 'space and time':
http://www.amazon.com/exec/obidos/tg...altimecolli-20. Is 3D rather than 2D, but it's (a hell of) alot easier to convert 3D stuff to 2D than the other way around.
But, I don't have masses of books, (infact, I only really have that book, and this one,
http://www.amazon.com/Calculus-Analy.../dp/0070576424, which is way to deep for what I tend to need), so perhaps there are more appropriate choices.
For basic 2D math.. A 'middle-level' education textbook should probably suffice.. In UK terms, an A-level or equivalent textbook should have enough material to understand most things you'd need to do w.r.t to 2D geometry, linear algebra, integration/differentiation, and that's a good basis for doing a whole lot of stuff.
Often, the hardest thing to work out is where & how to actually apply what you know, and what extra you'll need to know in order to do x. If you can classify exactly what x is, searching for how x is usually done, reading that material, following references / researching what you don't know, and recursing tends to work quite well, and you'll pick up useful transferable stuff along the way.
A quick question, what sort of mathematical architecture are you using? By that I mean, when you think about your code, do you think 'points and angles' or 'vectors and matrices'?
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And remember, mathematics is actually fun when you get the hang of it (spoken like a true geek I know...) 
