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Variable change in definite integration

  1. Mar 11, 2014 #1
    I am having trouble understanding how the author of the textbook "Physics for scientists and engineers" (Randall D Knight), is performing the variable change in the definite integral of the picture that I have taken a screen clipping of. Can someone please help me figure this out?
     

    Attached Files:

  2. jcsd
  3. Mar 11, 2014 #2
    Variable r is being replaced by variable u where

    u = z[itex]^{2}[/itex] + r[itex]^{2}[/itex].

    Hence

    [itex]\frac{du}{dr}[/itex] = 2r

    since z is a constant.
     
  4. Mar 11, 2014 #3
    thanks! I understand now
     
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