Results 1 to 5 of 5

Math Help - f'(x) with logs

  1. #1
    Junior Member
    Joined
    Oct 2008
    Posts
    35

    f'(x) with logs

    For each function f(x) , find f'(x)
    f(x)=log(9) [2^(x)+1]
    The 9 is subscript

    Guys I am lost on this lonely road please help me.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    12,126
    Thanks
    1009
    change of base formula ...

    \log_b(u) = \frac{\ln(u)}{\ln(b)}<br />

    \frac{d}{dx} \left[\frac{\ln(u)}{\ln(b)}\right] = \frac{1}{\ln(b)} \cdot \frac{u'}{u}

    this should be in your textbook.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Oct 2008
    Posts
    35
    so it would be
    d/dx [log(a) (f(x))]
    d/dx [ln(f(x))/ln(a)]
    f'(x) / f(x)ln(a)
    now im lost
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Junior Member
    Joined
    Oct 2008
    Posts
    35
    is that right
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    12,126
    Thanks
    1009
    f(x) = \log_9(2^x + 1)

    f'(x) = \frac{1}{\ln{9}} \cdot \frac{2^x \cdot \ln{2}}{2^x + 1}
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 9
    Last Post: February 22nd 2011, 06:39 PM
  2. Logs
    Posted in the Algebra Forum
    Replies: 4
    Last Post: April 24th 2010, 08:52 AM
  3. Logs
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: October 10th 2009, 07:08 PM
  4. Dealing with Logs and Natural Logs
    Posted in the Advanced Algebra Forum
    Replies: 0
    Last Post: April 14th 2008, 07:18 AM
  5. several questions-logs/natural logs
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: November 12th 2007, 09:58 PM

Search Tags


/mathhelpforum @mathhelpforum