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Maths C4 Integration Urgent

http://pmt.physicsandmathstutor.com/download/Maths/A-level/C4/Topic-Qs/Edexcel-Set-1/C4%20Integration%20-%20By%20parts.pdf

Q4C Page 3
MS is on the top of page 12

I did everything correctly up to the point where I had: ∫(u-1)^2/u
What I did was separated this into ∫(u-1)^2*1/u which I then integrated to ln(1+e^x) + 1/2(e^2x) after subbing back the x

I don't understand why my method is incorrect, I understand what the MS has done but not why my method doesn't work. Thanks in advance!

EDIT: I realise my answer doesn't show what the question wants me to show however why is my method incorrect?
@Notnek


Thanks in advance...
Original post by Wolfram Alpha
http://pmt.physicsandmathstutor.com/download/Maths/A-level/C4/Topic-Qs/Edexcel-Set-1/C4%20Integration%20-%20By%20parts.pdf

Q4C Page 3
MS is on the top of page 12

I did everything correctly up to the point where I had: ∫(u-1)^2/u
What I did was separated this into ∫(u-1)^2*1/u which I then integrated to ln(1+e^x) + 1/2(e^2x) after subbing back the x

I don't understand why my method is incorrect, I understand what the MS has done but not why my method doesn't work. Thanks in advance!

EDIT: I realise my answer doesn't show what the question wants me to show however why is my method incorrect?


How does (u1)21u.du\displaystyle \int (u-1)^2 \cdot \dfrac{1}{u}.du integrate to lnu+12(u1)2\ln u + \frac{1}{2}(u-1)^2 ?? Explain your thought process.
Reply 3
Original post by Wolfram Alpha
@Notnek


Thanks in advance...

I can’t help right now but you didn’t get an answer because you didn’t post in the maths forum. I’ve moved this thread for you now.
Original post by RDKGames
How does (u1)21u.du\displaystyle \int (u-1)^2 \cdot \dfrac{1}{u}.du integrate to lnu+12(u1)2\ln u + \frac{1}{2}(u-1)^2 ?? Explain your thought process.


I re-attempted the question and managed to get the correct answer - God knows what I tried to do the first time, but thanks a lot for your response!
Original post by Notnek
I can’t help right now but you didn’t get an answer because you didn’t post in the maths forum. I’ve moved this thread for you now.


Thanks for moving this for me :smile:.
Original post by RDKGames
How does (u1)21u.du\displaystyle \int (u-1)^2 \cdot \dfrac{1}{u}.du integrate to lnu+12(u1)2\ln u + \frac{1}{2}(u-1)^2 ?? Explain your thought process.


Irrelevant to the question in OP, but when integrating y^1/3 why doesn;t it integrate to ln(y^1/3)?
Reply 7
Original post by Wolfram Alpha
Irrelevant to the question in OP, but when integrating y^1/3 why doesn;t it integrate to ln(y^1/3)?

I think you’ll need to explain why you think it would. Have you tried differentiating ln(y^1/3)?
Original post by Notnek
I think you’ll need to explain why you think it would. Have you tried differentiating ln(y^1/3)?


Oh I see now :biggrin:
1/3yln(y)^2/3 =/= y^1/3

Thanks, I always forget to differetiate to check if it actually works.
Reply 9
Original post by Wolfram Alpha
Oh I see now :biggrin:
1/3yln(y)^2/3 =/= y^1/3

Thanks, I always forget to differetiate to check if it actually works.

I don’t know how you managed to get that when differentiating ln(y^1/3).
Original post by Notnek
I don’t know how you managed to get that when differentiating ln(y^1/3).


Had I integrated correctly, would the result have been 1/3y^2/3lny^1/3?

Isn;t it the case that for any function of x where y = lnf(x) the differentiated result would be f'(x)/f(x)?

so f'(lny^(1/3)) = (1/y)(1/3)(y^(-2/3))
thus the final result would be f'(x)/f(x) = (1/y)(1/3)(y^-2/3)/lny^1/3 but since there are fractions in the numerator this becomes

1
-----------------------
3y^(2/3)lny^(1/3)

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