I often see mathematical notation on Wikipedia articles (e.g. Finding the matrix of a transformation). Where is a good resource for learning what the different symbols mean?
You can check out the following wikipedia web page. It is a list of mathematical symbols and the associated $\LaTeX$ codes.
However I feel that in order for one to be truly accustomed to notation, you should read mathematics and try and figure out the notation as you go along. Gradually after a while you will build up a knowledge base of what certain symbols mean/ which conventions are employed.
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From your link, it looks like the stuff that is troubling you is related to vectors and linear algebra type notation. The best way to learn this stuff is from a general calculus book (up through multi-variable calculus). It really depends more on what you're getting stuck on. I agree with Benjamin, the best way to learn is by reading math and DOING math, because it's important to intuitively understand the symbols and what they represent. A good place to start might be the Stewart book, which covers Calc I, II and III.
After that, you'll want to start learning the algebraic notation which mostly comes from set theory and logic, so a book like this might help (this is just sort of a shot in the dark, I don't personally know anything about this book, but something like this). Much of this stuff you can probably find in books at a book store like Borders. Also, just Google things like "standard math notation, matrices" or something. There's lots of info online.