Which relation is a function?

a. {(1, 2); (2, 5); (3, 2); (4, 5)}

b. {(1, 2); (1, 3); (3, 2); (4, 2)}

c. {(1, 2); (2, 3); (3, 4); (1, 5)}

d. {(1, 2); (2, 3); (3, 4); (2, 5)}

Question

Which relation is a function?	
 
a. {(1, 2); (2, 5); (3, 2); (4, 5)}
 

b. {(1, 2); (1, 3); (3, 2); (4, 2)}
 
c. {(1, 2); (2, 3); (3, 4); (1, 5)}
 

d. {(1, 2); (2, 3); (3, 4); (2, 5)}

anonymous · Answer

I found it is A, thank you

mathmate · Answer

When the x-values are all different, the relation is a function.

When there are duplicated x-values, if the corresponding y-values are identical, then the relation is still a function.  If the y-values are different for the same x-values, then the relation is not a function.

Yes, A is a function.