4. which relation is a function?
o {(3, 4), (2, 4), (5, 1), (3,5)}
o {(3, 4), (3, 3), (1, 2), (1,5)}
{(1,4), (1, 3), (1, 2), (1, 1);
{(1, 3), (2, 6), (3,9), (4, 12)}

The last option choice [(1,3), (2,6), (3,9), (4,12)

Step-by-step explanation:

The key idea to understand in a function/relation is that each input can only have one output. Inputs are your x-variables and outputs are your y-variables.

In the first relation, you see the two points (3,4) and (3,5). 3 is your input [since its x] , however, it gives you two outputs [y's], 4 and 5. So you can cross out the first option.

In the second relation, look at the points (3,4) and (3,3). Again, both have the same input 3, but different outputs, 4 and 3. So you can cross out the second option.

In the third relation, look at all of the points. They all share a common input, 1, but different outputs, 2, 3, 4, and 5. So you can cross out the third option too.

Lastly, look at the last relation. They all have different inputs but the key thing to look at here is that each input only has one corresponding output. Thus, this is the right answer.

I hope this helps!