Question

Which relation is NOT a function?

{(10, –4), (–10, 14), (14, –10)}
{(–4, –10), (–2, –4), (–10, –1), (–1, –7), (1, 10), (–3, –1)}
{(–4, 10), (14, 3), (15, 14), (10, 3)}
{(11, 16), (12, 14), (14, 14), (11, 13), (21, 12)}

Answer 1

{(11, 16), (12, 14), (14, 14), (11, 13), (21, 12)}

This is because the the number 11, an x-value, is used twice and if an x-value is used more than once then it is not a function. A function is a relation between sets where there is only one output for each input