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Math Help - Help with partial derivative needed

  1. #1
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    Exclamation Help with partial derivative needed

    I have a function
    u(r,t)= (sin(kr-wt))/r

    How do I find the partial derivatives:

    du/dr
    d^2u/dr^2
    d^2u/dt^2

    Thanks in advance
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  2. #2
    Member Goku's Avatar
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    Re: Help with partial derivative needed

    u(r,t)= (sin(kr-wt))/r

    for \frac{du}{dr}

    treat "t" as a constant, and then find derivative.

    so

    we find:

    \frac{du}{dt}(r^{-1}sin(kr-wt))= -r^{-2}sin(kr-wt)+r.r^{-1}cos(kr-wt)
    = cos(kr-wt)- \frac{sin(kr-wt)}{r^{2}}

    Now from there solve the rest...
    Thanks from xmaoe123
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