What is the precise answer for integrating 3lnx/x?

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    Integration
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Discussion Overview

The discussion revolves around the integration of the expression 3lnx/x, focusing on the appropriate substitution and differentiation steps involved in solving the integral. The scope includes mathematical reasoning and problem-solving techniques related to integration.

Discussion Character

  • Mathematical reasoning, Homework-related

Main Points Raised

  • One participant seeks assistance in determining the correct substitution for the integral of 3lnx/x.
  • Another participant suggests that if solving for u, the expression could be rearranged as (x/3lnx)dx = du, proposing integration by parts.
  • A different participant questions the initial assumption of u being 3ln(x), indicating that more context is needed to understand the dependency of u on x.
  • A participant clarifies that they copied the problem and needed to find u and take it one step further, indicating a misunderstanding of the task.
  • One participant suggests that knowing the derivative of ln(x) could be helpful and proposes setting u = ln x, asking what du would be in that case.
  • Another participant responds with the derivative of ln(x), stating it should be 1/x, and emphasizes the need for precision in the expression.

Areas of Agreement / Disagreement

Participants express differing views on the correct approach to the problem, with no consensus reached regarding the appropriate substitution or method for integration.

Contextual Notes

Some participants indicate a lack of clarity regarding the problem's requirements and the relationship between u and x, which may affect the integration process.

Mitchtwitchita
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Can anybody help me out with this?

3lnx/x du = ( ? ) dx. What is the question mark? Leave no spaces in your answer.

I thought u was 3lnx, which would be make it 3/x dx. Apparently not. Can anybody show me the right way of doing this sort of problem please?
 
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Are you trying to solve for u? If so:

(x/3lnx)dx = du

You can integrate both sides, the left by integration by parts, I think will work.
 
That really makes no sense without knowing how u depends on x. Why did you "think u was 3ln(x)"? Are you leaving out part of the problem?
 
Sorry, I should have been more clear. I just copied and pasted the problem. The question was 3lnx/x, and I just needed to find the first part of the problem. The professor wanted us to "find u, and take it one more step." I thought that step was differentiating u. All I really need is what would be in the brackets with respect to dx.
 
Then knowing that the derivative of ln(x)= 1/x should help you! 3ln(x)/x dx= 3(ln x)(dx/x). I would incline toward setting u= ln x. What is du now?
 
1/x?
 
Mitchtwitchita said:
1/x?

should be 1/x dx precise.
 

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