Question

What's the inverse function of `y= -3`?

Answer 1

That function does not have an inverse function.

Explanation:

The function `f(x) = 3` is not one-to-one.
The graph of the function does not pass the horizontal line test.
If we know the output we cannot state the input uniquely.

The is no function `g` such the `g(f(x)) = x` for all real x.