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Math Help - Partial Derivatives...

  1. #1
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    Partial Derivatives...

    I'm having trouble with the concept. I need to find the partials dz/dy and dz/dx when z=ycos(x-y) and keep coming up with different answers... Can anyone help?
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  2. #2
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    Quote Originally Posted by abradfo1 View Post
    I'm having trouble with the concept. I need to find the partials dz/dy and dz/dx when z=ycos(x-y) and keep coming up with different answers... Can anyone help?
    With partial derivatives, you just treat all the variable as constants except the one you're differentiating with respect to.

    z_y = \cos(x-y) + y\sin(x-y)

    z_x = -y\sin(x-y)

    Your different answers may actually be the same. For instance, don't forget little things like that \cos(x-y) = \cos(y-x), and \sin(x-y) = -\sin(y-x). This could cause your answers to look different but still might all be correct.
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