Integrating with partial fractions and simpifying the answer

In summary, the conversation discusses how to find the definite integral of a given function using partial fraction decomposition. The speaker shares their attempt at a solution and receives feedback on a small error. The conversation concludes with a reminder to simplify and use properties of logarithms to arrive at the correct answer.
  • #1
tasveerk
24
0

Homework Statement


the definite integral of (x-1)/(x^3+4x^2+3x) from x=1 to x=3 using partial fraction decomposition. I know the answer should be (5/3)ln2 - ln3.


Homework Equations





The Attempt at a Solution


After integrating, I got -(1/3)ln(3x) - (2/3)ln(x+3) + ln(x+1) . The issue is that after I implement the limits of integration, I cannot seem to simplify it to get the answer (5/3)ln2 - ln3.
 
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  • #2
I believe your -(1/3)ln(3x) should be -(1/3)ln(x)
 
  • #3
tasveerk said:
After integrating, I got -(1/3)ln(x) - (2/3)ln(x+3) + ln(x+1) .

I agree with your result for the antiderivative (after fixing that "3x" ). One of the terms in the evaluation gives (1/3) ln 1 and so can be omitted. Be sure to consider that ln (6) = ln (2) + ln (3) and that ln ( 4 ) = 2 ln ( 2 ) . The stated answer appears to be correct.
 

Related to Integrating with partial fractions and simpifying the answer

1. What is the purpose of integrating with partial fractions and simplifying the answer?

The purpose of integrating with partial fractions is to break down a complex rational function into simpler fractions, which can then be integrated separately. Simplifying the answer allows us to express the integrated function in a more concise and manageable form.

2. How do you determine the partial fraction decomposition?

The partial fraction decomposition can be determined by first factoring the denominator of the rational function. Then, the coefficients of each term in the decomposition can be solved for using a system of equations. This involves setting up the original rational function and its partial fraction decomposition equal to each other and solving for the coefficients.

3. What are the steps for integrating with partial fractions?

The steps for integrating with partial fractions are as follows:

  1. Factor the denominator of the rational function.
  2. Write out the partial fraction decomposition using the coefficients found from solving the system of equations.
  3. Integrate each individual fraction using basic integration rules.
  4. Add the integrated fractions back together to get the final integrated function.

4. Can the final answer be simplified further?

Yes, the final answer can be simplified further by factoring out any common factors and canceling out any terms that are the same in both the numerator and denominator. This can be done to make the final answer as concise as possible.

5. Are there any cases where integrating with partial fractions is not necessary?

Yes, there are some cases where integrating with partial fractions is not necessary. If the rational function is already in a simple form that can be directly integrated using basic integration rules, then there is no need to use partial fractions. Additionally, if the denominator of the rational function cannot be factored, then partial fractions cannot be used and another method of integration must be used.

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