Question

Is (2,1), (1,-2), (-3,2), (2,-3) a function?

Answer 1

No - there are two distinct values for `f(2)`, so this relation does not describe a function.

Explanation:

A set of pairs `(x_i, y_i)` defines a function if

For all `i, j` we have `x_j = x_i => y_j = y_i`

This is trivially satisfied if all the `x_i`'s are distinct.

In our example, we have pairs `(2, 1)` and `(2, -3)` which break the condition.