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Homework Help: Very quick and easy question about integrating and completing the square

  1. Oct 11, 2011 #1
    1. The problem statement, all variables and given/known data

    The problem could be any variation of dx/(x2-2x)

    2. Relevant equations

    ∫dx/x2-a2 = 1/2a ln ((x-a)/(x+a)) + C

    3. The attempt at a solution

    I understand the answer to be 1/2 ln ((x-2)/x) + C

    My question is why is it just x on the bottom in the solution? Shouldnt it be x+2 since the equation states "x+a"? Similar to the way it is x-2 on the top which makes sense since the formula states "x-a". Any help is greatly appreciated.
  2. jcsd
  3. Oct 11, 2011 #2


    Staff: Mentor

    This integration formula isn't directly relevant to your problem. In this formula, the denominator is a difference of squares. In your problem, you don't have a difference of squares.

    You could manipulate your denominator to get a difference of squares, since
    x2 - 2x = x2 - 2x + 1 - 1 = (x - 1)2 = 1.
  4. Oct 11, 2011 #3
    Ah yes, I overlooked the minor details. Thank you.
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