Results 1 to 4 of 4

Thread: derivative

  1. #1
    Member
    Joined
    Feb 2010
    Posts
    98

    derivative

    yea so my tutor screwed this one up and she did it wrong.. can someone show a step by step for this derivative please.

    (x^3-2x)/(sqrt(2x+1))
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    14,782
    Thanks
    3006
    Quote Originally Posted by tbenne3 View Post
    yea so my tutor screwed this one up and she did it wrong.. can someone show a step by step for this derivative please.

    (x^3-2x)/(sqrt(2x+1))
    \frac{d}{dx} \frac{x^3-2x}{\sqrt{2x+1}} = \frac{\sqrt{2x+1} \cdot (3x^2-2) - (x^3-2x) \cdot \frac{1}{\sqrt{2x+1}}}{2x+1}

    multiply by \frac{\sqrt{2x+1}}{\sqrt{2x+1}} to clear the inner fraction ...

    \frac{(2x+1)(3x^2-2) - (x^3-2x)}{(2x+1)^{\frac{3}{2}}}<br />

    \frac{6x^3+3x^2-4x-2 - x^3 + 2x}{(2x+1)^{\frac{3}{2}}}

    \frac{5x^3 + 3x^2 - 2x - 2}{(2x+1)^{\frac{3}{2}}}
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Feb 2010
    Posts
    98
    thanks but i have a question.. did you chain rule the derivative of sqrt(2x+1)
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    14,782
    Thanks
    3006
    Quote Originally Posted by tbenne3 View Post
    thanks but i have a question.. did you chain rule the derivative of sqrt(2x+1)
    sure did ...

     <br />
\frac{d}{dx} (2x+1)^{\frac{1}{2}} = \frac{1}{2}(2x+1)^{-\frac{1}{2}} \cdot 2 = (2x+1)^{-\frac{1}{2}} = \frac{1}{\sqrt{2x+1}}<br />
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. contuous weak derivative $\Rightarrow$ classic derivative ?
    Posted in the Differential Geometry Forum
    Replies: 2
    Last Post: Apr 22nd 2011, 02:37 AM
  2. Replies: 0
    Last Post: Jan 24th 2011, 11:40 AM
  3. [SOLVED] Definition of Derivative/Alt. form of the derivative
    Posted in the Calculus Forum
    Replies: 2
    Last Post: Sep 23rd 2010, 06:33 AM
  4. Derivative of arctan in a partial derivative
    Posted in the Calculus Forum
    Replies: 3
    Last Post: Sep 12th 2010, 01:52 PM
  5. Replies: 2
    Last Post: Nov 6th 2009, 02:51 PM

Search Tags


/mathhelpforum @mathhelpforum