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.  

lunar landing mission. apollo 11 was the first manned mission to land on the moon. the first steps by humans on another planetary body were taken by neil armstrong and buzz aldrin on july 20, 1969. the astronauts also returned to earth the first samples from another planetary body.

explanation: