Results 1 to 10 of 10

Math Help - differentiate y = x(x+a)^1/2

  1. #1
    Junior Member
    Joined
    Oct 2007
    Posts
    32

    differentiate y = x(x+a)^1/2

    the original question was y = x squareroot x + 1

    answer in the back is (-2/3, -2 squareroot 3/9)

    EDIT: question is differentiate ^above^. Hence find the stationary point on the curve giving exact value.

    i pretty much get no were close
    sorry for not putting in the squareroot sign dont know how lol


    thx
    Last edited by KavX; November 3rd 2007 at 08:06 PM. Reason: didnt give out whole question
    Follow Math Help Forum on Facebook and Google+

  2. #2
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by KavX View Post
    the original question was y = x squareroot x + a

    answer in the back is (-2/3, -2 squareroot 3/9

    i pretty much get no were close
    sorry for not putting in the squareroot sign dont know how lol

    thx
    use the product rule

    recall that: \frac d{dx}f(x)g(x) = f'(x)g(x) + f(x)g'(x)

    thus, if we have y = x (x + a)^{\frac 12}

    \Rightarrow y' = x' \cdot (x + a)^{\frac 12} + x \cdot \left[ (x + a)^{\frac 12 } \right]'

    now continue
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Oct 2007
    Posts
    32
    yer i can get up to that part but i dont get what to do after and wateva i do i dont end up with the right answer the part i need help with is after that step
    Follow Math Help Forum on Facebook and Google+

  4. #4
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by KavX View Post
    yer i can get up to that part but i dont get what to do after and wateva i do i dont end up with the right answer the part i need help with is after that step
    you didn't tell me what you need to do after that, you just said differentiate ...

    what was the whole question?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Oct 2007
    Posts
    32
    woopz sorry it says differentiate ^above^. Hence find the stationary point on the curve giving exact value.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by KavX View Post
    woopz sorry it says differentiate ^above^. Hence find the stationary point on the curve giving exact value.
    so the derivative is given by:

    y' = \sqrt{x + a} + \frac x{2 \sqrt{x + a}}

    to find the stationary points, we set the derivative to zero, thus we have:

    \sqrt{x + a} + \frac x{2 \sqrt{x + a}} = 0

    multiply through by 2 \sqrt{x + a}, we get:

    2(x + a) + x = 0

    can you take it from here?
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member
    Joined
    Oct 2007
    Posts
    32
    aaahhh kool thanx, i forgot to say that a = 1 sorry,

    yer i can get the x value of -2/3

    2(x + 1) + x = 0
    2x + 2 + x = 0
    3x = -2
    x = -2/3

    but im not sure how to get x = 2
    Follow Math Help Forum on Facebook and Google+

  8. #8
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by KavX View Post
    aaahhh kool thanx, i forgot to say that a = 1 sorry,

    yer i can get the x value of -2/3

    2(x + 1) + x = 0
    2x + 2 + x = 0
    3x = -2
    x = -2/3

    but im not sure how to get x = 2
    who says x = 2? you said the answer was x = -2/3, which you got. to get the y-coordinate, just plug in x = -2/3 in the original expression (and plug in a = 1 as well) and solve for y
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Junior Member
    Joined
    Oct 2007
    Posts
    32
    sorry just that another answer above of that said it had -2/3 as a x value and x = 2. my bad just read the wrong answer, anywayz thanx for all your help
    Follow Math Help Forum on Facebook and Google+

  10. #10
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by KavX View Post
    sorry just that another answer above of that said it had -2/3 as a x value and x = 2. my bad just read the wrong answer, anywayz thanx for all your help
    well, x = 2 if a = -3.

    i don't know if you had to consider that case as well
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. can you differentiate e^(x/(3+5x)) ?
    Posted in the Calculus Forum
    Replies: 2
    Last Post: November 5th 2010, 02:52 PM
  2. differentiate tan^3[2x]
    Posted in the Calculus Forum
    Replies: 1
    Last Post: September 15th 2010, 05:07 AM
  3. differentiate
    Posted in the Calculus Forum
    Replies: 1
    Last Post: July 22nd 2010, 03:56 AM
  4. How do you differentiate e^xy?
    Posted in the Calculus Forum
    Replies: 3
    Last Post: February 28th 2009, 09:57 AM
  5. Differentiate with e^x
    Posted in the Calculus Forum
    Replies: 2
    Last Post: October 9th 2008, 08:21 PM

Search Tags


/mathhelpforum @mathhelpforum