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Help with expansion of an expression

  1. Oct 17, 2012 #1
    Hello,

    I have a problem to understand how the author made the following expansion:


    1/sqrt{1+[2(r-r')*d]/(r-r')^2}≈1-{[(r-r')*d]/(r-r')^2+....}

    where all the letters go for vectors and the symbol '*' is the dot product.
    I suppose it is a Taylor expansion, but i just don't get it in this case.


    Can someone give me the way?
     
  2. jcsd
  3. Oct 17, 2012 #2

    mfb

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    2016 Award

    Staff: Mentor

    1/sqrt(1+x) ≈ 1/(1+x/2) ≈ 1-x/2
    Two taylor expansions up to the linear term.
     
  4. Oct 18, 2012 #3
    thank you!
     
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