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Math Help - inverse function derivative

  1. #1
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    inverse function derivative

    find the value of d/dx(f^-1(x)) at x=2 when f(x)=2x-4
    (a)3
    (b)1/3
    (c)1/2
    (d)1/6

    my answer :1/2
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  2. #2
    MHF Contributor
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    Quote Originally Posted by gracy View Post
    find the value of d/dx(f^-1(x)) at x=2 when f(x)=2x-4
    (a)3
    (b)1/3
    (c)1/2
    (d)1/6

    my answer :1/2
    Yes, 1/2 is correct.

    That is easy.
    How come you were asking for the inverse of a cubic function before? That one is super hard. You have to use the Cubic Formula there.
    For Linear and Quadratic functions, getting their inverses, if they exist, is relatively easy.
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  3. #3
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    Quote Originally Posted by gracy View Post
    find the value of d/dx(f^-1(x)) at x=2 when f(x)=2x-4
    (a)3
    (b)1/3
    (c)1/2
    (d)1/6

    my answer :1/2
    Hello, Gracy,

    your answer is correct.

    f is a linear function therefore the inverse of f is a linear function too:

    f^{-1}:\ y=\frac{1}{2}x-2. The derivative of this function is a constant: 1/2.

    EB
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