Sigma notation, trig and functions are generally covered in pre-calculus, but I think to be on the safe side you will want to look at Calculus too at least for infinite series.
Books I would recommend
It would be best to cover pre calculus first, maths can be intimidating at times but honestly the more you learn the less you will feel discouraged, the best way to understand maths imo is through applications, its all well and truly nice being able to evaluate formulas but it all only truly makes sense when you see it applied to real life scenarios, Calculus books tend to be better at this as real life scenarios are usually changing
WOW! How can the authors of "Stewarts Pre-Calculus" justify price of 260$ for a book with 397 pages. Now thats a rip off if i ever seen one. Thanks for this advice, i gotta save for few months to get it....
EDIT: AH! Thank god for internet, got both books for "free".
I should also mention, James Stewart is often criticised for his methods in teaching both Calculus / Pre-Calculus, his Calculus book is a pain in the ass unless you already are comfortable with calculus, his pre calculus is not as bad but be warned it does not hold your hand, it will give you many examples + exercises but explain only what is necessary.
Now for me I like the way his pre-calculus book structure works, it gets straight to the point and theres often very little reading, but a lot of people have complained that it doesnt explain in detail, I dont think this is the purpose of the book but I do believe anyone new to concepts will understand, it just wont be as friendly, probably would explain the minimum.
As for book prices, typically e-books are cheaper and better to work with than paperback, not because of the environment, but because they are far easier to manage, search and bookmark.
As for piracy, I have mixed views on piracy, if the product is good and you are happy with it, buy it, however lets face it buying stuff these days is a gamble and returning is a pain, I dont want to start a piracy debate here, but the way I see it, the global return / refund policies are enough a reason why anyone should download pirated stuff, some people call it theft, some call it no risk sales, I dont of course download any pirated crap now though but dont have any issues with my past methods.
PS. The book should be over 1k pages, not sure what you were looking at :/