The answer checker generates a set of solutions from the provided formula ("+2pi n" by evaluating at n = -3..3), and generates a set of student "solutions" by evaluating at n = -10..10 (may be overkill, but needs to be at least twice the range because of the potential for "+ pi n" in the case of tangent). Each student value is checked as a solution to the given equation, and is also tested for overlap with the values from earlier expressions. Then, so long as the set of student values contains the set of actual solutions (and there are no incorrect values) the student should receive full-credit.
The issue that I'm still having is that even though my answer checker cleanly evaluates student responses for tangent equations, WeBWorK will complain if a student uses 1 formula (say pi/3 + pi n) instead of 2 (pi/3 + 2 pi n, 4 pi/3 + 2 pi n), or vice versa. Due to the inclusion of sine and cosine in the randomization of the problem, two formulas is the default for the list of correct answers.
TL;DR - can I override the requirement that the length of the student list match the length of the list provided as the answer?
see attached. (randomization to sine and cosine is disabled in the attached code for testing purposes)