# Can someone help me to work this integration?Watch

Thread starter 12 years ago
#1
Here's the problem.

Note: | = integral sign.

| xsin ax dx

How do I integrate it? I know the answer, but I can't prove it.

Can someone help, please?

Thank you very much!
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12 years ago
#2
By parts.

If | uv' dx = [uv] - |vu' dx

Let u = x, v' = sin(ax)
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Thread starter 12 years ago
#3
Thanks for that! The formula I was using was wrong, it seems. I used:

If | uv' dx = [uv] - |v dx

Thanks!
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12 years ago
#4
It is derived from the product rule.

(uv)' = u'v + u(v')

Integrate both sides gives you

[uv] = |u'v + |v'u

Then you rearrange to get the 'usual form' for integration by parts.
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