1. Disregard my comment. Since R is said to be a relation from A to B, we take both a ∈ A and b ∈ A. Then the set R is the pairs (a, b) whose entries' sum belongs to B.
We have
• 4 = 1 + 3 = 2 + 2 = 3 + 1, so R contains (1, 3), (2, 2), and (3, 1)
• 5 = 1 + 4 = 2 + 3 = 3 + 2 = 4 + 1, so R contains (1, 4), (2, 3), (3, 2), and (4, 1)
• 6 = 1 + 5 = 2 + 4 = … = 5 + 1, so R contains (1, 5), (2, 4), …, (5, 1)
Then
R = {(1, 3), (1, 4), (1, 5), (2, 2), (2, 3), (2, 4),
… (3, 1), (3, 2), (3, 3), (4, 1), (4, 2), (5, 1)}
2. The domain of R is the set of all values a in the pairs (a, b) belonging to R :
dom(R) = {1, 2, 3, 4, 5}
3. The range of R is the set of all values b in those same pairs:
range(R) = {1, 2, 3, 4, 5}
4. The inverse of R is the set with the same elements as R, but the entries are swapped:
inv(R) = {(3, 1), (4, 1), (5, 1), (2, 2), (3, 2), (4, 2),
… (1, 3), (3, 2), (3, 3), (1, 4), (2, 4), (1, 5)}
In this case, we have R = inv(R).
