Algebra 1, 2 – functions

Q: Which of the following represents a function?  (Choose all correct answers.)
 
a. {(4,2), (6,2), (-1,5), (3,-2), (-4,-7)}
b. {(4,2), (5,1), (-1,5), (5,-2), (4,-2)}
c. {(-1,-1), (1,1), (4,4), (3,3), (6,6)}
d. {(1,2), (3,2), (5,2), (7,2), (9,2)}
 
Answer: a, c, and d
Explanation:  A function must have only one y-value for each x-value.  Choice b has two points with the same x:  (4,2) and (4, -2) (and also two others).  All of the other choices have no repeated values for x, so they are functions.
 
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