Finally, a math question I can solve! You can determine if a relation is a function if you first understand what a relation is: A collection of ordered pairs.
Example:
(4,2),(2,2),(12,0), (9,1) etc.
Ordered pairs consist of input (x) values and output (y) values. In the example (4,2), four would be the x or input value. 2 would be the y or output value.
Once you understand that, all you need to do is look at YOUR specific relation. Look at all the x values in your relation. Are there two of the same input values? If this is the case, your relation is NOT a function. That's how easy it is :)