Congrats on being accepted to the program.

No idea about the best book, but one of the best things I did some time ago, was to log in to khanacademy.org, and started doing some courses to re-learn a few things.

Even things from algebra I and II, and trigonometry were interesting to re-learn.

Now I'm reading some GIS projection code, and watching movies on calculus & trigonometry to refresh on integrals, matrix calculus, and sine/cosine.

Maybe try Khan Academy and check the textbooks for some CS programs in universities.

Best of luck!