Which relation is a function?
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A function is a relation that for each input, there is only one output.

Here are mappings of functions. The domain is the input or the x-value, and the range is the output, or the y-value.

Each x-value is related to only one y-value.

Athough the inputs equal to -1 and 1 have the same output, this relation is still a function because each input has just one output.

This mapping is not a function. The input for -2 has more than one output.

I hope that helps. I don't know if it is right or wrong, but good luck :)