Algebra functions help?

Question

it's really basic algebra but i don't understand it. i will give you an example:

Input Output

2 5

4 6

6 5

8 6

I need to know if it is a function or not. (NOTE: please do not just give me an answer, tell me how to work it out)

Answer 1

All of the numbers have to be different. For example:

the ordered pairs are (2,5) (4,6) (6,5) and (8,6)

Since the 2 goes with the 5 but the 6 ALSO goes with the 5, its not a function. if it were a different number for either of them, say, (2,5) and (6,9) then it would work.

and the same thing goes for the (4,6) (8,6)

they can't both be with the six.

hope i helped.