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Find the inverse of this function

  1. Apr 22, 2014 #1


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    1. The problem statement, all variables and given/known data
    Let f be a function defined as f:(0,exp-3/2) → [-1/4, ∞),
    [itex] f(x) = (ln x)^2 + 3 ln x + 2 [/itex] then inverse of f is equal to

    3. The attempt at a solution

    The two possibilities are
    [itex]exp (\dfrac{-3\pm\sqrt{4x+1}}{2}) [/itex]

    How to decide which one is correct?
  2. jcsd
  3. Apr 22, 2014 #2
    Try plugging ##x=2## in the inverse function. That should help you in figuring out the correct sign.
  4. Apr 22, 2014 #3


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    Or note that one of your choices is always negative.
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