Question

determine whether the given function is one-to-one. if it is, find it's inverse: f(x)=-1

Answer 1

one to one means:

if f(x1)=f(x2) then x1=x2, but f(1)=f(2)=-1 and 1 is not 2, so your function is not one to one.

Answer 2

also we have the horizontal line test, and your function itself is a horizontal line, so it fails the horizontal line test infinitely many times