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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


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    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!
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