# What have I done wrong here?Watch

#1
This integral does not have antiderivative that is elementary. However, when I attempted it (before knowing the functions nature) I was able to get an elementary antiderivative. Which tells me something in my method must be wrong?

My working is below. Apologies for the handwriting.
Last edited by Bangz; 3 weeks ago
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#2
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3 weeks ago
#3
(Original post by Bangz)
This integral does not have antiderivative that is elementary. However, when I attempted it (before knowing the functions nature) I was able to get an elementary antiderivative. Which tells me something in my method must be wrong?

My working is below. Apologies for the handwriting.
After a quick look I can't see how you've arrived at this

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#4
(Original post by Notnek)
After a quick look I can't see how you've arrived at this

Via integration by parts. I let U be xe^x and my dV be lnx - 1
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3 weeks ago
#5
Bangz I can see that your IBP explanation is below the working (which is confusing!). I'll have another look.
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3 weeks ago
#6
(Original post by Bangz)
Via integration by parts. I let U be xe^x and my dV be lnx - 1
Surely it's not that.

You differentiated the entire thing for some reason instead of integrating it.

dv/dx becomes v through integration, but ln(x)-1 becomes 1/x through differentiation...

Last edited by RDKGames; 3 weeks ago
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#7
(Original post by RDKGames)
Surely it's not that.

You differentiated the entire thing for some reason instead of integrating it.

Aaaah thanks. Stupid mistake.
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3 weeks ago
#8
Too slow

Bangz try to make sure your working is consistent, especially when showing it to someone else. Your "Let u(x) = ..." sometimes appeared above the IBP and sometimes below which was very confusing!
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#9
(Original post by Notnek)
Too slow

Bangz try to make sure your working is consistent, especially when showing it to someone else. Your "Let u(x) = ..." sometimes appeared above the IBP and sometimes below which was very confusing!
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