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Partial diffrentiation HELP

  1. Oct 15, 2007 #1
    Partial diffrentiation....URGENT PLZ HELP

    Here are the two problems.......

    1- If U=(X,Y) X=F(R,S) Y=G(R,S)

    SHOW THAT: Urr=(Wxx) (Fr)^2 + 2(Wxy) (Fr) (Gr)^2 + (Wx) (Frr) + (Wy)+ (Grr)


    2- SHOW THAT: U(R,K)=R^n Cos(nk) satisfies the equation
    Urr+1/r U + 1/(r^2) Ukk=0


    that's urgent plz help now if u can.....thanks
     
  2. jcsd
  3. Oct 17, 2007 #2

    cristo

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    You need to show some work before we can help you. Also, what is W in the first question? You have not defined it! For the second one, you simply take the required derivatives of U and plug then in.
     
  4. Oct 17, 2007 #3

    HallsofIvy

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    Use the chain rule- twice.
     
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