For AMS 2: "Prerequisite(s): Mathematics 2 or placement exam score of 20 or higher."
For AMS 3: "Prerequisite(s): score of 20 or higher on Mathematics Placement Exam or Mathematics 2."
For Math 3: "Prerequisite(s): course 2 or placement exam score of 20 or higher."
For classes being offered Spring, Summer or Fall 2012, it is easiest to search the online schedule at https://pisa.ucsc.edu/class_search/index.php
to see what the prerequisites for classes are. Make sure you include Status "All Classes" to list the closed classes so you can look at all the class descriptions.
It looks like Math 3 = AMS 3, both Precalculus.