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-   -   Implicit differentiation (https://www.askmehelpdesk.com/showthread.php?t=65302)

  • Feb 22, 2007, 11:27 AM
    nickie6038
    Use implicit differentiation to find y' :

    xe^xy=y


    Use implicit differentiation to find y':

    xln y = y^3 - 2


    Use implicit differentiation to find y''(x) at the point (5,1):

    x^3 + y^3 = 126

    Use implicit differentiation to find the slope of the tangent line to the given curve at (-1,-2):

    e^y+13-e^2=5x^2+2y^2

    Use implicit differentiation to find y':

    2y^3 + y^2 - 2x^2 = -14
  • Feb 22, 2007, 11:38 AM
    Capuchin
    I've merged all of your questions into a single post, since they are on the same topic.

    Why don't you have a go first, and then we can help you with any problems you have.

    How have you tried to tackle it so far?
  • Feb 22, 2007, 12:07 PM
    asterisk_man
    nickie, can you double check the first equation. It seems to me that what you've entered is ambiguous.
    Do you mean

    or


    I guess that you probably mean the second one since the answer to the first one is trivial.
  • Feb 22, 2007, 12:08 PM
    nickie6038
    sorry I did start to answer one let me know if I'm doing something wrong?

    y'lny + xy = 3y^3y'
    xy-3^3y+2 = -ylny
    y'(x-3y^3+2) = -ylny
    y' = -ylny / x-3^3+2


    ?
  • Feb 22, 2007, 12:11 PM
    nickie6038
    sorry if I was ambiguous but yes it is
    x(e^xy)=y
  • Feb 22, 2007, 12:20 PM
    nickie6038
    Use implicit differentiation to find y’’(x) at the point (5,1):

    x^3 + y^3 = 126

    3x^2 + 3y^2 y' = 0

    y' = -3x^2/ 3y^2

    y' = -75/3

    y' = -25??
  • Feb 22, 2007, 12:25 PM
    nickie6038
    Use implicit differentiation to find y’:

    2y^3 + y^2 - 2x^2 = -14


    y' 6y^2 + 2y -4x = -14

    y' = 4x - 14 / 6y^2 + 2y

    ??
  • Feb 22, 2007, 12:26 PM
    nickie6038
    Is anyone here anymore?
  • Feb 22, 2007, 01:32 PM
    galactus
    Is that or ?
  • Feb 22, 2007, 01:45 PM
    galactus
    Quote:

    Originally Posted by nickie6038
    Use implicit differentiation to find y’’(x) at the point (5,1):

    x^3 + y^3 = 126

    3x^2 + 3y^2 y' = 0

    y' = -3x^2/ 3y^2

    y' = -75/3

    y' = -25 ?????????


    You need the 2nd implicit derivative, if I read correctly.

    You must differentiate again.



    Quotient rule:





    But,



    Factor:



    See, the in there? That equals 126.

    Finish up?
  • Feb 22, 2007, 02:08 PM
    asterisk_man
    you did:
    2y^3 + y^2 - 2x^2 = -14
    y' 6y^2 + 2y -4x = -14

    you made 2 errors.
    first, y^2 => y' 2y not 2y
    second, -14 => 0

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