Math Is Fun Forum

viorelbadicu

Member

Registered: 2010-07-15

Posts: 1

Very difficult Integral... Please Help

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

∫(exp(-ax)*cos(b*x))dx

Thanks a lot

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Very difficult Integral... Please Help

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.

soroban

Member

Registered: 2007-03-09

Posts: 452

Re: Very difficult Integral... Please Help

. .

.

. .

. .

. . . . . .

. . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . .

.

Hello soroban

Guest

Re: Very difficult Integral... Please Help

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

Re: Very difficult Integral... Please Help

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.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Very difficult Integral... Please Help

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.

Cosmopolite

Member

Registered: 2011-01-04

Posts: 6

Re: Very difficult Integral... Please Help

Thank you.