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Simple multivariable problem w/ ellipse

  1. Nov 27, 2011 #1
    1. The problem statement, all variables and given/known data

    If u=x^3 + 3xy + y^3, determine du/dx on the ellipse 2x^2+3y^2=1

    2. The attempt at a solution

    Imagine I just use partial derivative somehow, but I'm not sure what the question is asking by on the ellipse. I have a feeling its just something simple that I'm overlooking. Any help is appreciated. Thanks
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Nov 27, 2011 #2

    HallsofIvy

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    Science Advisor

    The chain rule:
    [tex]\frac{du}{dx}= \frac{\partial u}{\partial x}+ \frac{\partial u}{\partial y}\frac{dy}{dx}[/tex]
    You get dy/dx from the requirement that [itex]2x^2+ 3y^2= 1[/itex], of course.
     
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