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# Quick C3 integration

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1. Was hoping someone could help on this please, integrating with limits 1 to 9

I pulled out the 36 from the numerator , and made it:

After subbing in the limits I get the answer wrong as the answer given involves 12 pi ?

I got 36Pi ln25 , answer is 12Pi ln25 , I thought my method would usually work for these.
2. When you're integrating lnf(x), what's the rule?
3. The format has to be f'(x)/f(x). So you have to take out 12, as then you're left with 3 at the top (the bottom differentiates to 3). You should be fine from there on out.
4. notice you need a third of it
5. (Original post by RajPopat94)
When you're integrating lnf(x), what's the rule?
If it's 1/something, then ln(something) right ? , but I took out the 36 as a constant so that shouldn't matter ?
6. (Original post by Tulian)
If it's 1/something, then ln(something) right ? , but I took out the 36 as a constant so that shouldn't matter ?
7. I totally forgot about the 1/a part after taking the 36 out.

Thanks everyone

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