# Integration by parts

#1
Hi, I was trying this question from madas maths, but I'm not sure how to do it as whichever term I put as u and dv/dx, I always end up having to integrate something of the style e^x(trig(x))
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#2
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1 month ago
#3
(Original post by Cuspake)
If you do integration by parts twice ...
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1 month ago
#4
This integral is pretty interesting and classic. I'll start you off by letting I="the integral".
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#5
(Original post by tonyiptony)
This integral is pretty interesting and classic. I'll start you off by letting I="the integral".
As in letting 1 = dv/dx?
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#6
(Original post by mqb2766)
If you do integration by parts twice ...
What should I put as u and dv/dx please?
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1 month ago
#7
(Original post by Cuspake)
What should I put as u and dv/dx please?
One is the exponetial, the other is the trig term.
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1 month ago
#8
(Original post by Cuspake)
As in letting 1 = dv/dx?
As mqb2766 suggests, one is the trig, the other is the exponential. It really doesn't matter either case.
Now if you let I="the integral", something interesting happens if you IBP twice. Try it!
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#9
Do I use 1 as the integral both times round?

(Original post by tonyiptony)
As mqb2766 suggests, one is the trig, the other is the exponential. It really doesn't matter either case.
Now if you let I="the integral", something interesting happens if you IBP twice. Try it!
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1 month ago
#10
In cases where you get back your intial integral just replace it with I, that way you can get rid of it since I would always be your initial integral
Last edited by orion reid; 1 month ago
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1 month ago
#11
(Original post by orion reid)
...
Best to let the OP have time to work through their problems, as per the forum guidelines. Can you delete pls.
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#12
(Original post by orion reid)

I have attached a picture of a worked solution.
In cases where you get back your intial integral just replace it with I, that way you can get rid of it since I would always be your initial integral
Ohhh, thank you, that makes a lot of sense, thank you. I now understand what replacing the integral with I actually means aha
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1 month ago
#13
(Original post by mqb2766)
Best to let the OP have time to work through their problems, as per the forum guidelines. Can you delete pls.
Aye aye
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