From the preface to the book, which you can (usually) see on Amazon,
"Except for Chapter 8, the student need only know basic high-school algebra and geometry and introductory trigonometry in order to read this book. In fact, we believe that high-school seniors who are interested in mathematics could read much of this book on their own. To read Chapter 8, students should have a knowledge of elementary calculus."
For the record, the book has some mixed reviews on Amazon (which you might want to read).
For what it's worth, in principle I think I agree with the book's overall approach, but it might be tricky to pull-off. Be sure to use other study sources (good advice in any regard), which you can find, for example, here. In particular I recommend the books by Strang and the book by Hefferon for a first course.