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How would I expand this?

  1. Aug 31, 2012 #1
    1. The problem statement, all variables and given/known data

    r1 = √(L2+(y-0.5d)2)
    r2 = √(L2+(y+0.5d)2)
    Show that in the limit that both y and d are <<L r2 - r1 = yd/L

    2. Relevant equations

    3. The attempt at a solution

    r2 - r1 =(√(L2+(y+0.5d)2)) - (√(L2+(y-0.5d)2))

    Nevermind, I've figured it out but can't seem to be able to delete this post :s
    Last edited: Aug 31, 2012
  2. jcsd
  3. Sep 1, 2012 #2

    Simon Bridge

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    I'd have tried substituting x=[(y-0.5d)/L]2 and used the binomial approximation.
    Oh you figured it out - rather than delete the post - how about posting your result: that way others who get stuck can benefit.
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