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Math Help - solve for f -1

  1. #1
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    Exclamation solve for f -1

    hey guys
    i had a problem and i just need someone to check if the answer is right

    Find the value of d f -1/dx at x =f(a)

    f(x) = 4x + 9, a = -2

    i got 1/4 for the answer, is that right?
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  2. #2
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    Re: solve for f -1

    Quote Originally Posted by ubhutto View Post
    hey guys
    i had a problem and i just need someone to check if the answer is right

    Find the value of d f -1/dx at x =f(a)

    f(x) = 4x + 9, a = -2

    i got 1/4 for the answer, is that right?
    since the inverse of f(x) is a linear function with slope = 1/4, your solution is correct.

    for the general case, if f(x) and g(x) are inverse functions, then ...

    f[g(x)] = x

    \frac{d}{dx} \left(f[g(x)] = x\right)

    f'[g(x)] \cdot g'(x) = 1

    g'(x) = \frac{1}{f'[g(x)]}
    Thanks from ubhutto
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  3. #3
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    Re: solve for f -1

    thanks alot
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