Results 1 to 6 of 6

Math Help - Derivative problem...how did they get this answer?

  1. #1
    Member
    Joined
    Dec 2008
    Posts
    92

    Derivative problem...how did they get this answer?

    http://i43.tinypic.com/2j11mgy.jpg --> problem is here

    I only would like to know how they got that from the derivative equation. Can you please show me step by step how you'd go about doing it, using that formula?

    Thanks!!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Eater of Worlds
    galactus's Avatar
    Joined
    Jul 2006
    From
    Chaneysville, PA
    Posts
    3,001
    Thanks
    1
    They did this:

    \lim_{h\to 0}\frac{\frac{1}{\sqrt{x+h}}-\frac{1}{\sqrt{x}}}{h}

    How, work the algebra magic, take the limit as h approaches 0 and you have it. The derivative of \frac{1}{\sqrt{x}}



    Note: I used h instead of {\Delta}x. Same thing
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Dec 2008
    Posts
    92
    I got that too but I don't understand what comes next..can you please show me the next steps?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Jester's Avatar
    Joined
    Dec 2008
    From
    Conway AR
    Posts
    2,361
    Thanks
    39
    Quote Originally Posted by galactus View Post
    They did this:

    \lim_{h\to 0}\frac{\frac{1}{\sqrt{x+h}}-\frac{1}{\sqrt{x}}}{h}

    How, work the algebra magic, take the limit as h approaches 0 and you have it. The derivative of \frac{1}{\sqrt{x}}



    Note: I used h instead of {\Delta}x. Same thing
    Next hint, simplify what Galactus has as

    \lim_{h\to 0}\frac{\sqrt{x}-\sqrt{x+h}}{h\sqrt{x+h}\sqrt{x}} then rationalize.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Dec 2008
    Posts
    92
    I did that and got your answer but now I'm having trouble rationalizing...could you show me how to go about that with this problem?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor
    Jester's Avatar
    Joined
    Dec 2008
    From
    Conway AR
    Posts
    2,361
    Thanks
    39
    Quote Originally Posted by janedoe View Post
    I did that and got your answer but now I'm having trouble rationalizing...could you show me how to go about that with this problem?
    <br />
\lim_{h\to 0}\frac{\sqrt{x}-\sqrt{x+h}}{h\sqrt{x+h}\sqrt{x}}  = \lim_{h\to 0}\frac{\sqrt{x}-\sqrt{x+h}} {h\sqrt{x+h}\sqrt{x}}\cdot \frac{\sqrt{x}+\sqrt{x+h}}{\sqrt{x}+\sqrt{x+h}}

    Expand only the numerator and things in the top will cancel, then cancel the h in the bottom, then take the limit.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: September 20th 2010, 09:47 AM
  2. Partial derivative answer check please.
    Posted in the Calculus Forum
    Replies: 0
    Last Post: July 1st 2010, 08:24 PM
  3. Is my answer for derivative right
    Posted in the Calculus Forum
    Replies: 6
    Last Post: April 27th 2009, 03:04 PM
  4. derivative check answer please!
    Posted in the Calculus Forum
    Replies: 2
    Last Post: September 8th 2008, 02:15 AM
  5. Please Check my Answer Derivative
    Posted in the Calculus Forum
    Replies: 2
    Last Post: March 21st 2007, 05:31 PM

Search Tags


/mathhelpforum @mathhelpforum