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Math Help - Inverse function

  1. #1
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    Inverse function

    If f(x) = ln 4x, what is the value of f^-1(6). (The f raises to the -1 is the inverse function of f(x).

    The answer is 100.86.
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  2. #2
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    Re: Inverse function

    So, let y = ln(4x). How, in general, do you invert functions?
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  3. #3
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    Re: Inverse function

    The natural log (ln) has a base e, so another way of rewriting f(x) = ln 4x or y = ln 4x:
    e^{y} = 4x
    \frac{e^{y}}{4} = x

    y = 6. Substituting it into this equation and solving for x will yield approximately 100.86.
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