Question

Which relation is a function?
A. (1, 0), (3, 0), (1, 1), (3, 1) (1, 3)
B. (1, 1), (2, 2), (3, 3), (4, 4), (5, 8)
C. (2, 7), (6, 5), (4, 4), (3, 3), (2, 1)
D. (9, −3), (9, 3), (4, −2), (4, 2), (0, 0)

Answer 1

B. Every x-value in B (1,2,3,4,5) appears exactly once, so each input has a single output — it is a function.