Results 1 to 3 of 3

Math Help - Finding the derivative

  1. #1
    Junior Member
    Joined
    Sep 2009
    Posts
    32

    Finding the derivative

    Hi guys...I'm having some troubles with this one question and it's really starting to bug me cause I keep getting it wrong.

    The question is:




    So, I tried simplifying it...

    v = (9*x^1/2 + 5/(3*x^1/3))^2
    v = (9x^1/2 + 5/(3x^1/3))^2
    I then distributed the 2 from outside the brackets into the brackets, so:
    v = (81x + 25/9x^2/3)
    Then I took the derivative...
    v(der) = 81 + 25/6x^-1/3

    Should I have done something with the 25 on the top of that fraction? I'm really not sure.

    Thanks in advance.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    11,683
    Thanks
    446
    Quote Originally Posted by dark-ryder341 View Post
    Hi guys...I'm having some troubles with this one question and it's really starting to bug me cause I keep getting it wrong.

    The question is:




    So, I tried simplifying it...

    v = (9*x^1/2 + 5/(3*x^1/3))^2
    v = (9x^1/2 + 5/(3x^1/3))^2
    I then distributed the 2 from outside the brackets into the brackets, so: v = (81x + 25/9x^2/3)

    can't do that ... \textcolor{red}{(a+b)^2 \ne a^2 + b^2} ... you know better, don't you?
    if you're trying to find \frac{dv}{dx}, just use the chain rule. expanding that binomial is just going to make a bigger mess.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Sep 2009
    Posts
    12
    I really doubt you're expected to have to multiply that out. So just use the chain rule as the previous poster suggested.

    n(a + b)^n-1*(da/dx + db/dx)
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Help finding derivative
    Posted in the Calculus Forum
    Replies: 6
    Last Post: June 29th 2010, 08:00 PM
  2. Finding the Derivative...
    Posted in the Calculus Forum
    Replies: 1
    Last Post: March 2nd 2010, 08:39 AM
  3. Finding the third derivative
    Posted in the Calculus Forum
    Replies: 1
    Last Post: February 18th 2009, 07:43 PM
  4. Finding the derivative
    Posted in the Calculus Forum
    Replies: 2
    Last Post: February 3rd 2009, 07:57 AM
  5. Finding the value of the derivative.
    Posted in the Calculus Forum
    Replies: 6
    Last Post: February 10th 2008, 10:17 AM

Search Tags


/mathhelpforum @mathhelpforum