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Homework Help: Zwiebach page 210

  1. Oct 26, 2007 #1
    1. The problem statement, all variables and given/known data
    Zwiebach claims that differentiating 12.12, which is

    [tex]X^I (\tau, \sigma) X^J(\tau, \sigma')-X^J(\tau, \sigma') X^I(\tau, \sigma) = 0[/tex]

    w.r.t. tau gives the same commutator with everything dotted. I think that is downright wrong. If you use the product rule to write everything out, it just doesn't work out.

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 26, 2007 #2
    Apply equation (12.21) to the second equation in the first line of equations (12.12).
  4. Oct 26, 2007 #3
    You also have to use 12.1 to get the leftmost part, don't you?
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