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Math Help - Functions

  1. #1
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    Functions

    Find f'(x)
    don't know how to slove this

    3) f(x) = log9(2^x + 1)

    the 9 is subscript
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  2. #2
    MHF Contributor Mathstud28's Avatar
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    Quote Originally Posted by bigton View Post
    Find f'(x)
    don't know how to slove this

    3) f(x) = log9(2^x + 1)

    the 9 is subscript
    \frac{d}{dx}\bigg[\log_a\left(f(x)\right)\bigg]=\frac{d}{dx}\bigg[\frac{\ln\left(f(x)\right)}{\ln(a)}\bigg]=\frac{f'(x)}{f(x)\ln(a)}
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  3. #3
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    so what rule is this and do i just sub
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  4. #4
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    Quote Originally Posted by theflyingcow View Post
    so what rule is this and do i just sub
    That used many rules. If you have to take the derivative of something in the exact form of y=\log_{a}f(x), then yes you can substitute. But this isn't worth memorizing, I promise you.
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  5. #5
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    so subing into the variables into the equation is the answer
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  6. #6
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    For this problem, yes.
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