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Lagrangian Derivation

  1. Jan 7, 2014 #1
    I have been reading Lagrangian from Classical Mechanics by John R. Taylor.
    I have adoubt in a derivation which invloves differential calculus.

    I have attached snapshot of the equation , can someone please explain.
    Here y,η are fucntions of x but α is s acosntant.

    Please let me know if I am not clear.

    Attached Files:

    • L.PNG
      File size:
      3.5 KB
  2. jcsd
  3. Jan 7, 2014 #2


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    Gold Member

    This is a simple application of the Chain Rule for Partial Derivatives.

    If you have a little bit of time, you could derive it by going back to the definition of the derivative.
    You would simply inject a variation of α and calculate the variation of the expression.
  4. Jan 8, 2014 #3
    Not sure how to go about it , can you please explain.
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