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Homework Help: Partial derivatives; Tangent Planes

  1. Apr 19, 2014 #1
    Hi guys,

    Question is:

    Find the slopes of the curves of intersection of surface z = f(x,y) with the planes perpendicular to the x axis and y axis respectively at the given point.

    z = 2x2y ...at (1,1).

    fx(x,y) = 4xy ∴ Slope = 4
    fy(x,y) = 2x2 ∴ Slope = 2

    Is this wrong?

    Answer has it the other way around fx = 2 and fy =4

    what mistake did i make?

  2. jcsd
  3. Apr 19, 2014 #2


    Staff: Mentor

    Your work looks fine. It looks like they switched the values in the "answer" you showed.
  4. Apr 19, 2014 #3
    I thought so too, thanks!
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