Results 1 to 5 of 5

Math Help - derivative.. problem

  1. #1
    Senior Member
    Joined
    Sep 2009
    Posts
    300

    derivative.. problem

    hello

    I need some help with finding the derivative of 4x(squareroot 1-x^2)

    Please look at the drawing, the correct answer is in green ,I cant seem to get it?
    Please help
    Thanks
    Attached Thumbnails Attached Thumbnails derivative.. problem-presproblem.jpg  
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Dec 2009
    Posts
    3,120
    Thanks
    1
    Hi wolfhound,

    just use a combination of the product rule and chain rule to solve.

    \frac{d}{dx}4x\sqrt{1-x^2}=4x\frac{d}{dx}\sqrt{1-x^2}+\sqrt{1-x^2}\frac{d}{dx}4x

    =(4x)0.5(1-x^2)^{-0.5}(-2x)+\sqrt{1-x^2}(4)

    =\frac{-4x^2}{\sqrt{1-x^2}}+\frac{4(1-x^2)}{\sqrt{1-x^2}}

    since \frac{\sqrt{1-x^2}\sqrt{1-x^2}}{\sqrt{1-x^2}}=\frac{1-x^2}{\sqrt{1-x^2}}
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Jan 2010
    Posts
    29
    Quote Originally Posted by wolfhound View Post
    hello

    I need some help with finding the derivative of 4x(squareroot 1-x^2)

    Please look at the drawing, the correct answer is in green ,I cant seem to get it?
    Please help
    Thanks
    y=4x\sqrt{1-x^2}

    y'=4\sqrt{1-x^2}+4x(\frac{1}{2}(1-x^2)^{-\frac{1}{2}}\cdot -2x)
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Senior Member
    Joined
    Sep 2009
    Posts
    300
    Thanks , But I still cannot finish the question to find the answer in the green,
    how do I do this?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor
    Joined
    Dec 2009
    Posts
    3,120
    Thanks
    1
    The final two fractions now have a common denominator, wolfhound.
    They can now be added to get the result in green.

    See my earlier post and how the denominators are made equal.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Derivative Problem
    Posted in the Calculus Forum
    Replies: 1
    Last Post: September 28th 2010, 08:37 PM
  2. Derivative Problem
    Posted in the Calculus Forum
    Replies: 6
    Last Post: August 27th 2010, 05:02 AM
  3. derivative.. problem
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 13th 2010, 05:29 AM
  4. Derivative problem.
    Posted in the Advanced Statistics Forum
    Replies: 2
    Last Post: July 12th 2009, 06:58 AM
  5. Derivative problem
    Posted in the Calculus Forum
    Replies: 3
    Last Post: April 13th 2008, 01:41 AM

Search Tags


/mathhelpforum @mathhelpforum