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Math Help - Question on derivative

  1. #1
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    Question on derivative

    hi everyone,

    Find \frac{dz}{dx} and \frac{dz}{dy}
    xyz-cos(x+y+z)=0


    i am having problems with the cos(x + y + z).

    Thank you in advance for all your help & support.
    Last edited by anderson; March 2nd 2010 at 11:31 AM.
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  2. #2
    Super Member General's Avatar
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    Quote Originally Posted by anderson View Post
    hi everyone,

    Find \frac{dz}{dx} and \frac{dz}{dy}
    xyz-cos(x+y+z)=0


    i am having problems with the cos(x + y + z).

    Thank you in advance for all your help & support.
    What is your problems exactly in cos(x+y+z) ?
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  3. #3
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    hi General,

    is this correct?

    F(x,y,z) = xyz - cos(x + y + z)

    F_x=yz+sin(x+y+z),

    i dont know how to get sin(x+y+z), u = (x + y + z),i dont know how to continue from there to get sin(x+y+z)

    thank you for all your help & support.
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  4. #4
    Member Miss's Avatar
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    Quote Originally Posted by anderson View Post
    hi General,

    is this correct?

    F(x,y,z) = xyz - cos(x + y + z)

    F_x=yz+sin(x+y+z),

    i dont know how to get sin(x+y+z), u = (x + y + z),i dont know how to continue from there to get sin(x+y+z)

    thank you for all your help & support.

    Sorry I will reply to this. Since General is offline.

    Your F_x is correct.

    In general, If h is differentiable, then:
    \frac{\partial}{\partial x}( \,\ cos( \, h(x,y,z) \, ) \,\ ) = -sin( \, h(x,y,z) \, ) \, \frac{\partial}{\partial x}( \, h(x,y,z) \, ).

    Did you get it ?
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