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Standard Product Rule?

  1. Dec 20, 2006 #1

    I'm having trouble following the following derivation I have seen in a text book:

    The derivation goes as follows:


    This is a Poisson eqn for P3 with respect to L0 which requires



    <L1P2>=.5<L1.phi(y)>.x^2. d^2P0/dx^2


    L(BS)(sigma).P1=.5<L1.phi(y)>.x^2. d^2P0/dx^2 eq 1

    <L1.phi(y).>=sqrt(2).p.v.<f(y).phi`(y)>.x. d/dx - sqrt(2).v<A(y)phi`(y)>. eq 2

    now according to the derivation when you substitute eq 2 into 1 you get:

    <L1.phi(y).>=sqrt(2)/2.p.v.<f(y).phi`(y)>.x^3. d^3/dx^3 +(sqrt(2).p.v.<f
    (y).phi`(y)> - sqrt(2)/2.v<A(y)phi`(y)>).x^2. d^2/dx^2 eq 3

    now it seems from the above that the x in:

    x. d/dx . x^2.d^2P0/dx^2

    is treated like a constant while the product rule is just applied to the d/dx . x^2.d^2P0/dx^2 part.

    Is this correct? If so can someone please explain why the x^2 and the x term are not grouped together?
  2. jcsd
  3. Dec 21, 2006 #2
    You might want to consider using tex and /tex tags to make this more readable.

    Sorry for not providing any help with the problem. I'm not even sure what your notation means! ( < > for instance)
  4. Dec 21, 2006 #3


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    Second the motion: clarify your notation. LaTex is nice but not necessary but you certainly need to explain your notation.
  5. Jan 28, 2007 #4
    OK will do is there a guide to using Latec on this Forum?
  6. Jan 28, 2007 #5


    User Avatar
    Staff Emeritus
    Science Advisor

    Yup, here's the link to the tutorial: https://www.physicsforums.com/showthread.php?t=8997. Please also remember to define your notation!
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