Which of the following sets represents a function?
{(3,5), (-1, 7), (3, 9))
{(1, 2), (3, 2), (5, 7))
{(1, 2), (1, 4), (1, 6)}

B. {(1, 2), (3, 2), (5, 7))

Explanation – Set B represents a function because all the first elements are different. While in the rest of the given sets, the first elements are repeated. In set A, 3 is repeated twice in the first element and in set C, 1 is repeated all the tree times in the first element.

While drawing it in a graph, one line may cross the other line which says that the given set is not a function. Such type of test is called as vertical line test.  

if you look up in the top right corner you'll see your current profile picture, click than click "view profile" you'll be able to change it there.