Final answer:
The sets a = {1, 2} and b = {2, 1} are considered equal in set theory because they contain the same unique elements, with order and repetition not being relevant.
Step-by-step explanation:
If a = 1, 2 and b = 2, 1, the question at hand is whether the sets a and b are equal. In set theory, two sets are considered equal if they contain exactly the same elements, regardless of the order in which they are listed. Sets do not account for the order of elements or repeated elements, meaning that the set {1, 2} is indeed the same as the set {2, 1} as they contain the same unique elements. Therefore, the sets a and b are equal.