Very quick and easy question about integrating and completing the square

  • Thread starter twisted079
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  • #1
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Homework Statement



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

Homework Equations



∫dx/x2-a2 = 1/2a ln ((x-a)/(x+a)) + C

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.
 

Answers and Replies

  • #2
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Homework Statement



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

Homework Equations



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

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.
 
  • #3
25
1
Ah yes, I overlooked the minor details. Thank you.
 

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