I have shown how to draw an inverse if you're given the graph, and how to find an inverse if you're given the formula. But suppose you are given two functions and told to verify (to check) that they are inverses of each other.
Now suppose your function is { (1, 2), (2, 1), (3, 4), (5, 1) }. The inverse of this function is { (2, 1), (1, 2), (4, 3), (1, 5) }. This inverse has two points, (1, 2) and (1, 5), that share a common x-value but have different y-values. This means that the inverse is NOT a function.