1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Inverse function

  1. Apr 26, 2010 #1
    1. The problem statement, all variables and given/known data
    Find the inverse function for f(x) = x + 4/x

    2. Relevant equations

    3. The attempt at a solution
    I tried many times but just can't get the answer.
    Is there any trick to this question?

    Thank you
  2. jcsd
  3. Apr 26, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Basically, what you want to do, is solve
    y = 4x + 4/x
    for x.
    Secretly, you can view this as a quadratic equation. You can either multiply through by x, then this becomes immediately apparent.

    If you're looking for a more general approach, I suggest combining the two fractions (4x/1 and 4/x) on the right hand side into a single fraction A/B, then you can cross-multiply (y = A/B becomes yB = A).

    In both cases, you can get an equation of the form
    ax2 + bx + c = 0
    the solution(s) of which give an inverse function.
  4. Apr 26, 2010 #3
    Ahh!!! Why didn't I think of that. Thanks!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook