Question

what is an inverse function

Answer 1

it is easier to define first an inverse relation
that means if you have a function say
f = { (1,2) (3,5) (4,7) }

the inverse *relation* switches x and y
f inv = {(2,1) ( 5,3) (7,4)}

Answer 2

now sometimes when you do inverse relation, it is also a function (but sometimes it isn't)

Answer 3

can you find a function whose inverse relation is not a function ?