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**viorelbadicu****Member**- Registered: 2010-07-15
- Posts: 1

Could somebody help me with this integral??? I need it as soon as possible

∫(exp(-ax)*cos(b*x))dx

Thanks a lot

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi viorelbadicu;

Hi;

From Pierce's short table of integrals # 431.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**soroban****Member**- Registered: 2007-03-09
- Posts: 452

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**Hello soroban****Guest**

I tried to solve it by parts but instead of using cos(bx) as u, I chose e^(-3x) and cos(bx) as my dv. I got a completely different answer but I would like to know if what I got is correct. My messy answer was: e^(-ax)[ 1/(b^2+a^2)sin(bx)]-[a/(b^3++ba^2]cos(bx)+C. Sorry for all the parenthesis. Thank you:(

**Cosmopolite****Member**- Registered: 2011-01-04
- Posts: 6

It was me that made the precedent post. I redid the work correctly using e^(-3x) as my u and cos(bx) as my dv and I got the same answer than you guys.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi Cosmopolite;

That is very good and welcome to the forum!

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**Cosmopolite****Member**- Registered: 2011-01-04
- Posts: 6

Thank you.

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