I suck at math, please divulge resources

Read this page to learn more about cosines.

http://en.wikipedia.org/wiki/Unit_circle

This is great advice. I did EE and I don't think it was until about the 2nd or 3rd year that we got a treatment of systems and signals that was sufficient to understand DCT. You seem to be focusing on the cosine part but it turns out that the cosine part of the DCT is probably the easiest part to understand. It probably won't make much sense until 1) you understand something about discrete signals and 2) you understand why transforms from one domain to another are particularly useful for solving certain problems.

I recommend 'Linear Systems and Signals' by B.P. Lathi. It was the book I used. It doesn't cover DCT explicitly, but it does have a friendly, Knuth-like treatment of the history of the mathematics. It makes for a nice break between sections of heavily technical material. Here is an excerpt from the beginning of the book on the topic of complex numbers and why they are useful. It should give you an idea what the rest (and the general subject) is like:

"If we want to travel from City a to City b (both in Country X), the shortest route is through Country Y, although the journey begins and ends in Country X. We may, if we desire, perform this journey by an alternate route that lies exclusively in X, but this alternate route is longer. In mathematics, we have a simliar situation with real numbers (Country X) and complex numbers (Country Y). All real-world problems must start with real numbers, and all the final results must also be in real numbers. But the derivation of results is considerable simplified by using complex numbers as an intermediary. It is also possible to solve all real-world problems by an alternate method, using real numbers exclusively, but this would increase the work needlessly."

Actually, it's easy: time. Just put in the hours.

If you want specific books, you need to say what your current level is, which you kind of explained, but much more importantly, what exactly you want to do. While most math is useful, different fields have different bodies of math I'd learn first: machine learning vs stats vs algorithmic optimization vs 3d graphics vs fluid dynamics vs financial mathematics, etc. I'll try to watch this post and put up book recommendations if you are specific.

Also, the last thing to note is unlike most other subjects, math is cumulative. Calculus is really easy, and almost thing new, if you understand trigonometry and algebra. Seriously, only like 10% new material. The trick is math rewards really deeply understanding subjects and penalizes you for not doing so. Learning half the material but deeply understanding it is, IMO, more valuable than the reverse.

Google books could be your friend here. Sounds to me like you might benefit from a physics 101 type text, such as Halliday and Resnick. All these types of books will have a section on waves and their applications in the real world. Some, on fourier series too. Some of these books will have a preview mode on google books (though not Halliday & Resnick). Try to find the ones that do.

Dont worry, all good programmers I know have sucked at maths at one point or the other. Try sage http://www.sagemath.org/ , its a free software written in python. The software has a web interface which lets you program the equations and see visual output in form of graphs or other suitable figures.

Have a look at sage demo at http://wiki.sagemath.org/interact and try it after downloading. If you still have issues, write back, we would love to help you...