Question

Which function has an inverse that is also a function?
{(–4, 3), (–2, 7), (–1, 0), (4, –3), (11, –7)}
{(–4, 6), (–2, 2), (–1, 6), (4, 2), (11, 2)}
{(–4, 5), (–2, 9), (–1, 8), (4, 8), (11, 4)}
{(–4, 4), (–2, –1), (–1, 0), (4, 1), (11, 1)}

Answer 1

Of all these functions: 

{(–4, 3), (–2, 7), (–1, 0), (4, –3), (11, –7)}

{(–4, 6), (–2, 2), (–1, 6), (4, 2), (11, 2)}

{(–4, 5), (–2, 9), (–1, 8), (4, 8), (11, 4)}

{(–4, 4), (–2, –1), (–1, 0), (4, 1), (11, 1)}

The only one which has an inverse that is also a function is:

{(–4, 3), (–2, 7), (–1, 0), (4, –3), (11, –7)}

These others do not have inverses which are also functions:

{(–4, 6), (–2, 2), (–1, 6), (4, 2), (11, 2)}

{(–4, 5), (–2, 9), (–1, 8), (4, 8), (11, 4)}

{(–4, 4), (–2, –1), (–1, 0), (4, 1), (11, 1)}