Help with simple integration problem

  • Thread starter CaityAnn
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  • #1
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Solve y'= Ln(12x)



Homework Equations


Integral of ln(x)= xlnx-x dx


The Attempt at a Solution


12x*ln(12x)-12x dx or even xlnx-x*1/12
But Im pretty sure these are wrong.

My calculator gives me xlnx+(ln(12)-1)x wth? Help!
 

Answers and Replies

  • #2
492
1
do you know how to do integration by parts?
in order to solve this problem you need to use it.
 
  • #3
cristo
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Solve y'= Ln(12x)



Homework Equations


Integral of ln(x)= xlnx-x dx


The Attempt at a Solution


12x*ln(12x)-12x dx or even xlnx-x*1/12
But Im pretty sure these are wrong.
Yup, they are incorrect.

To do this, you should note why the integral of ln(x) is equal to xlnx-x dx. Namely, we use integration by parts, writing the integrand as 1.ln(x). So, for your question, we have [tex]\int \ln(12x) dx=\int 1\cdot\ln(12x) dx [/tex]. Now, can you see a suitable choice for "u" and "dv" to enable you to perform integration by parts on this?

My calculator gives me xlnx+(ln(12)-1)x wth?
Your calculator is correct. [When you have the answer, check to see if yours is the same as this]
 
  • #4
Kurdt
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Science Advisor
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Try substituting 12x = u and work from there.

EDIT: Damn my slowness. And also cristo's method is better, mine is rather lazy.
 
Last edited:

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