Calc II Partial Fractions with Natural Logs

In summary, the conversation is about finding the integral of \frac{dx}{x(1+ln x)} and the initial attempt at solving it using partial fractions. The conversation then discusses the possibility of using a substitution and someone suggests letting u=1+ln x. It is also mentioned that the use of partial fractions may not be appropriate for this problem since the integrand is not a rational function.
  • #1
demersal
41
0

Homework Statement



[tex]\int[/tex][tex]\frac{dx}{x(1+ln x)}[/tex]

Homework Equations


Partial Fractions? Maybe I am solving this wrong...


The Attempt at a Solution



[tex]\frac{A}{X}[/tex] + [tex]\frac{B}{1+ln x}[/tex] = 1

A(1+lnx) + Bx =1
A + Alnx + Bx =1

This doesn't seem to work out properly. I have been having a lot of trouble understanding partial fractions so any help in assisting me in making this first step of the problem would be greatly appreciated! Even if partial fractions aren't the correct way to go about this, if you could explain how you knew what to do, I think it would help me a lot in the long run! Thanks!
 
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  • #2
I don't think you can use partial fractions like that since the integrand is not a rational function.

Try a substitution, let u=1+ln x
 
  • #3
let u=lnx
 
  • #4
ignore me! i was sick :(
 
  • #5
rocomath said:
ignore me! i was sick :(

Your sub still works too
 

Related to Calc II Partial Fractions with Natural Logs

What is the purpose of using partial fractions with natural logs in Calc II?

The purpose of using partial fractions with natural logs in Calc II is to simplify complex algebraic expressions involving logarithmic functions. This technique involves breaking down a fraction with a natural log in the denominator into simpler, more manageable fractions.

How do you determine the coefficients of the partial fractions with natural logs?

The coefficients of the partial fractions with natural logs can be determined by setting up a system of equations using the original fraction and its decomposed form. The equations can then be solved using algebraic techniques to find the values of the coefficients.

What are the steps for decomposing a fraction with a natural log in the denominator?

The steps for decomposing a fraction with a natural log in the denominator are as follows:
1. Factor the denominator into linear and quadratic terms.
2. Set up a system of equations using the original fraction and its decomposed form.
3. Solve the system of equations to find the values of the coefficients.
4. Rewrite the original fraction as a sum of the decomposed fractions.
5. Integrate each fraction separately to find the final solution.

Can partial fractions with natural logs be used for any type of fraction with a logarithmic function?

No, partial fractions with natural logs can only be used for fractions with a single natural log in the denominator. If a fraction has multiple logarithmic functions or a combination of different logarithmic functions, a different approach such as the method of undetermined coefficients must be used.

Are there any special cases or exceptions when using partial fractions with natural logs?

Yes, there are a few special cases when using partial fractions with natural logs. If the denominator has a repeated linear factor, the corresponding coefficient in the decomposed fraction will be a polynomial of a higher degree. Additionally, if the denominator has complex roots, the coefficients in the decomposed fractions will also have complex values.

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