Results 1 to 5 of 5

Math Help - can someone please just double check

  1. #1
    Newbie
    Joined
    Jul 2008
    Posts
    9

    can someone please just double check

    I just want to make sure I am doing this correctly

    d/dx(e^5x + 1) = 5e^5x

    and

    find d2/dx2 (lnx)^3 = 6(lnx)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Mathstud28's Avatar
    Joined
    Mar 2008
    From
    Pennsylvania
    Posts
    3,641
    Quote Originally Posted by 10164064 View Post
    I just want to make sure I am doing this correctly

    d/dx(e^5x + 1) = 5e^5x

    and

    find d2/dx2 (lnx)^3 = 6(lnx)
    Second one is wrong

    Remember

    \frac{d}{dx}\bigg[f(g(x))\bigg]=f'(g(x))\cdot{g'(x)}
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Rhymes with Orange Chris L T521's Avatar
    Joined
    May 2008
    From
    Santa Cruz, CA
    Posts
    2,844
    Thanks
    3
    Quote Originally Posted by 10164064 View Post
    I just want to make sure I am doing this correctly

    d/dx(e^5x + 1) = 5e^5x

    and

    find d2/dx2 (lnx)^3 = 6(lnx)
    The first one is correct.

    However, the second one is missing something...

    \frac{d^2}{dx^2}(\ln(x))^3

    You need to apply the chain rule here...

    \frac{d}{dx}(\ln(x))^3=3(\ln(x))^2\cdot\frac{1}{x}  =\frac{3(\ln(x))^2}{x}

    \frac{d}{dx}\frac{3(\ln(x))^2}{x}=\frac{6\ln(x)-3(\ln(x))^2}{x^2}

    Hope this makes sense!

    --Chris
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Jul 2008
    Posts
    9
    its to the second derivative right?
    so is it
    {6/x(lnx)}-{3(lnx)^2/x^2}
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Jul 2008
    Posts
    9
    Ok thanx for the clarification Chris.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. can someone double check this for me?
    Posted in the Calculus Forum
    Replies: 6
    Last Post: July 18th 2010, 01:55 PM
  2. Double Check
    Posted in the Calculus Forum
    Replies: 5
    Last Post: November 15th 2009, 05:11 PM
  3. Double check
    Posted in the Calculus Forum
    Replies: 4
    Last Post: October 24th 2009, 10:18 PM
  4. double check
    Posted in the Algebra Forum
    Replies: 1
    Last Post: October 21st 2008, 10:03 AM
  5. Double check please
    Posted in the Calculus Forum
    Replies: 2
    Last Post: June 4th 2006, 07:09 PM

Search Tags


/mathhelpforum @mathhelpforum