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Trying to find dy/dx of a trig function # 2

  1. Oct 30, 2011 #1

    jtt

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    1. The problem statement, all variables and given/known data
    find dy/dx


    2. Relevant equations
    x+tanxy=0


    3. The attempt at a solution
    d/dy(x+tanxy)

    x+sec^2(xy)((1)(dy/dx))+(1)(tanxy)=0
    dy/dx(sec^2(xy)+x+tanxy=0
    -x-tanxy -x-tanxy
    dy/dx(sec^2(xy)/(sec^2(xy)=(-x-tanxy)/(sec^2(xy))

    dy/dx=(-x-tanxy)/(sec^2xy)
     
  2. jcsd
  3. Oct 30, 2011 #2

    LCKurtz

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    You can begin by stating the problem unambiguously. Are you trying to differentiate

    x + tan(xy) = 0 or x + ytan(x)=0. The point is that as it is written we can't tell whether the y is inside or outside that tangent function. Parentheses are necessary!
    Why are you writing d/dy when you are differentiating with respect to x?
     
  4. Oct 30, 2011 #3

    jtt

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    trying to differentiate x+tan(xy)

    i got dy/dx when i took the derivative of y in tan(xy)
     
  5. Oct 31, 2011 #4

    LCKurtz

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    You mean d/dx(x + tan(xy))

    Is the derivative of x equal to x??

    And what I highlighted in red should be the derivative of the (xy) which is the argument of the tangent function, or the "inside". There should be no tan(xy) in that.
     
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