Question

Which relation is a function?
A. (-25,16), (0,16), (-25,18)
B. (19,11), (34,12), (34,10)
C. (35,31), (24,15), (12,0)
D. (34,30), (18,17), (34,15)

Answer 1

A function is a relation where for every 1st coordinate, there is only one possible 2nd coordinate. For example (1,2) and (1,3) is NOT a function because for 1st coordinate "1" there are two possible values, 2 and 3.

Answer 2

There is one option above where this is NOT the case. Look for duplicate 1st coordinates -- those are NOT functions.