Precalculus: Concepts Through Functions (A Unit Circle Approach To Trigonometry), 3rd edition by Sullivan and Sullivan. Its ISBN is 978-0-134-30810-4. This is a PCC custom edition of a book with the same name with ISBN 978-0-321-93104-7. Either version is acceptable.

Having unrestricted access to a textbook is a requirement. You may own a copy or borrow one from a friend for the term. Used copies are fine and are often less expensive when bought online or at Powell's Building 2. Earlier editions of the same book may be acceptable. However you must understand that exercises usually change from one edition to the next, and sometimes the chapters change content or order. If you have an older edition, contact me to discuss if it will be acceptable.