Question

Which relation is a function?

{0, –9, –2, –3}
{(0, –9), (–9, 0), (–3, –3)}
{(0, –9), (–9, –2), (0, –3)}
{(0, –9), (–2, –3), (–2, 0), (–3, –2)}

Answer 1

the first one is out

Answer 2

for the next three, pick the one with no repeats in the first coordinate

Answer 3

for example, not this one
{(0, –9), (–2, –3), (–2, 0), (–3, –2)}
because the -2 repeats