Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Right Inverse?

  1. Dec 30, 2008 #1


    User Avatar
    Gold Member

    Could someone please explain what is implied if a function has a right inverse? Thanks.
  2. jcsd
  3. Dec 30, 2008 #2
  4. Dec 30, 2008 #3
    Let f be a function.

    If r is the right inverse of f, then for all x, f(r(x)) = x. That is, the composition of f and r, f * r, is the identity function.

    If l is a left inverse of f, then for all x, l(f(x)) = x. Again, this means l * f is the identity function.

    If a function g is both a left and a right inverse, it is called a full inverse (or just simple, THE inverse). The full inverse of of f is usually designated f-1.

    Some examples:

    The squaring function, f(x) = x^2, is not one-to-one, and so it has no full inverse. However, it does have a partial inverse (a left inverse) which is the square root function. We know this because sqrt(x^2) = x. We can show it is not a full inverse by demonstrating that for some x, (sqrt(x))^2 /= x, and we can let x be any negative number. (Note in the complex numbers, sqrt is in fact a full inverse).
  5. Dec 30, 2008 #4


    User Avatar
    Gold Member

    NoMoreExams: Thanks, I had not read that article. That clears a lot of things up.

    Tac-Tics: Thanks for the example.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook