Very quick and easy question about integrating and completing the square

In summary, the conversation discusses a problem involving integrating dx/(x2-2x) and finding the solution using a given formula. It is noted that the denominator is not a difference of squares, but it can be manipulated to become one. The correct solution is determined to be 1/2 ln ((x-2)/x) + C, with an explanation for the discrepancy in the denominator.
  • #1
twisted079
25
1

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.
 
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  • #2
twisted079 said:

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.
twisted079 said:

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
Ah yes, I overlooked the minor details. Thank you.
 

FAQ: Very quick and easy question about integrating and completing the square

What is the purpose of integrating and completing the square?

The purpose of integrating and completing the square is to simplify and solve quadratic equations. By completing the square, the quadratic equation can be written in the form y = a(x-h)^2 + k, which makes it easier to find the vertex and other key points on the graph.

How do you complete the square?

To complete the square, follow these steps:
1. Make sure the coefficient of the squared term is 1.
2. Move the constant term to the other side of the equation.
3. Take half of the coefficient of the x-term and square it.
4. Add this value to both sides of the equation.
5. Factor the perfect square trinomial and simplify.
6. Rewrite the equation in the form y = a(x-h)^2 + k.

Why is completing the square useful in integration?

Completing the square is useful in integration because it can help convert a rational function into the standard form of a partial fraction, making it easier to integrate. It can also be used to transform a difficult integral into a simpler one.

Can completing the square be used for any quadratic equation?

Yes, completing the square can be used for any quadratic equation. However, it is most useful for equations where the coefficient of the squared term is 1, as this makes the process simpler.

Are there any other methods for solving quadratic equations?

Yes, there are other methods for solving quadratic equations such as factoring, using the quadratic formula, and graphing. However, completing the square is a useful technique for solving equations that cannot be easily factored or for finding the vertex of a parabola.

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