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How to solve this limit? (difference of two square rooted terms)

  1. Aug 5, 2010 #1
    do you have a hint on how to solve this limit?

    [tex]\lim_{x\to +\infty}(\sqrt{x^2+ax+b}-\sqrt{x^2-ax+b})[/tex]

  2. jcsd
  3. Aug 5, 2010 #2
    When I see an expression of the form

    [tex]\sqrt{A} - \sqrt{B}[/tex]

    I think of multiplying it by

    [tex]\frac{\sqrt{A} + \sqrt{B}}{\sqrt{A} + \sqrt{B}}[/tex]

    Does that help?

  4. Aug 5, 2010 #3
    Thanks a lot!
    that trick made the job. The limit of that expression is a
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