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Implicit Differentiation

  1. Feb 20, 2008 #1
    [SOLVED] Implicit Differentiation

    -4x^2+3xy+4y^3=-328

    This is at the point (3,-4)
    and i am trying to find m


    2. Relevant equations



    3. The attempt at a solution

    here is my work

    -4x^2+3xy+4y^3=-328
    -8x+3xy'+3y+12y^2y'=0
    -8x+3y=-3xy'-12y^2y'
    -8x+3y=[-3x-12y^2]y'
    y'=(-8x+3y)/(-3x-12y^2)
    plug in x=1,y=3 then solve and get
    m=-12/67
    can you find the error?
    It would be very much appreciated
    thank you.
     
    Last edited: Feb 20, 2008
  2. jcsd
  3. Feb 20, 2008 #2

    nicksauce

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    Try plugging in the values to your final expression again.
     
  4. Feb 20, 2008 #3
    0h, the answer is correct, it just needs to be not negative, thank you. i was about to go crazy
     
    Last edited: Feb 20, 2008
  5. Feb 20, 2008 #4

    cristo

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    I don't agree that your numerical answer is correct, regardless of the sign.
     
  6. Feb 20, 2008 #5
    yeah, its correct i just checked. thankx for helping me:smile:
     
  7. Feb 21, 2008 #6

    cristo

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    Well, maybe it is now you've changed the point to (3,-4)!
     
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