Question

Are these functions or not?​

Answer 1

Answers:

1. Not a function
2. Not a function
3. Function
4. Not a function

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Explanation:

A function has any given input lead to exactly one output.

Relation 1 has the input "paper" lead to more than one output, which are the values 9 and -3. Therefore, relation 1 is not a function.

Relations 2 and 4 are similar stories.

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In contrast, relation 3 has each input lead to exactly one output, which is why we have a function here.

Put another way: a function cannot have the x coordinates repeat, but the y coordinates can repeat.