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    Hi all,

    Attached is an image of the question, i'm stuck on part iv) have no idea how I can go about it really. Any help would be appreciated!

    Name:  1357245177618.jpg
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    Damn it, the picture is too small.

    Basically if f(x) is 4x(2x-1)^7 anf f(1) = 4

    then what is d/dx(f^-1(x)) when x = 4
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    The derivative at the point x = a is given by

    \displaystyle \frac{df^{-1}}{dx} = \frac{1}{\displaystyle \frac{df}{dx}}

    where you evaluate \displaystyle \frac{df}{dx} at the point x = f^{-1}(a).
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    (Original post by jack.hadamard)
    The derivative at the point x = a is given by

    \displaystyle \frac{df^{-1}}{dx} = \frac{1}{\displaystyle \frac{df}{dx}}

    where you evaluate \displaystyle \frac{df}{dx} at the point x = f^{-1}(a).
    So do I work out the inverse of 4x(2x-1)^7? that seems way too complicated?
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    (Original post by Robskeh)
    So do I work out the inverse of 4x(2x-1)^7?
    Derivative. After that, you need to use f^{-1}(4).
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    (Original post by Robskeh)
    Hi all,

    Attached is an image of the question, i'm stuck on part iv) have no idea how I can go about it really. Any help would be appreciated!

    Name:  1357245177618.jpg
Views: 65
Size:  118.1 KB
    Where does the question come from, I have not seen one like this on any C4 paper?

    I found this helpful http://archives.math.utk.edu/visual....e.1/index.html

    So my solution is:

 
 
 
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