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waterskier2007's avatar

What is the integral of xe^(-x) dx?

Asked by waterskier2007 (2050points) September 10th, 2008

yeah, the integral

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33 Answers

Knotmyday's avatar

Sorry, my fingers and toes only go to 20.

shrubbery's avatar

let me get my maths folder out, two seconds

shrubbery's avatar

I think it would just be…. xe^(-x) + c

kevbo's avatar

not sure, but the integral of e to the x equals the function of u sub n. (write it down)

sarapnsc's avatar

Right when I think I am pretty smart, I see a question like this, and get knocked down a couple of notches, make that a couple, couple notches.
Looks like a foreign language to me!

waterskier2007's avatar

i found it out its -xe^(-x)(x+1)+c

Allie's avatar

True. No, Fasle. Yeah, false. Wait… what? Definitely true. I think.

gailcalled's avatar

@sarah: It is a foreign language (Calculus); you’d learn it just like you’d tackle French 1, slowly, methodically, and daily.

sarapnsc's avatar

@gail, not me….I’ll stick with French, french wasn’t anything like that, it was fun to learn!

Algebra & statistic was hard enough, I’ll leave the calculus to you and the rest of the brains here….I have math phobia bad!

gailcalled's avatar

@sarah; this question is like starting your first day of French by having to learn the subjunction of *pouvoir.” When you start at the beginning with pre-calculus, it is fun and clear and becomes magical, in its own weird way.

sarapnsc's avatar

@gail…pre-calculus????????? I barely made it through pre-algebra!

I don’t want to learn it…I have been traumatized enough from math! lol :)

gailcalled's avatar

Okay, I will cancel your registration.

sarapnsc's avatar

@gail lol, I needed that laugh, after seeing that other horrid thing that was posted earlier. Thanks for the laugh! hahaha

gailcalled's avatar

(Erk! I meant the “subjunctive”.)

critter1982's avatar

@waterskier2007: You’re right. I just pulled out my old calc 2 book and that example was in one of the chapters.

La_chica_gomela's avatar

Saranapnsc, maybe you should focus on English. “Algebra and Statistics were hard enough…”

;-)

cyndyh's avatar

@waterskier2007: Now take the derivative of what you got with respect to x and see if that works out for you. :^>

What you want to look for is “integration by parts”.

waterskier2007's avatar

yeah i did take the derivative just to check. thanks

cyndyh's avatar

Then you need to recheck your work because you’re a bit off. Cheers!

waterskier2007's avatar

no, im not a bit off. i just did it and it works. and i got the right answer using it

cyndyh's avatar

Nope. You have an extra x in your answer. If you want to work it through I’ll tell you where you’re going wrong.

waterskier2007's avatar

ah yeah for sure the extra x at the beginning. my bad indeed

cyndyh's avatar

No problem. Are you just learning about integration by parts? I’m just wondering why you asked this question in particular.

waterskier2007's avatar

no im in calc 4: diff eq but couldnt remember how to do that

La_chica_gomela's avatar

Anytime I have an integral I don’t feel like actually doing, I go to Wolfram.

La_chica_gomela's avatar

(By the way, TimothyKinney actually just typed that. I showed him the problem, and he is such a geek that he could not resist writing something). Feel free to give me his lurve though ;-) !! The way I see it, he donated it to me when he answered a question on my account.

cyndyh's avatar

Ha! I love Mathematica. I knew my fella loved me when he got me that for my birthday one year. It meant he “got” me. Cheers! :^>

cyndyh's avatar

@waterskier2007: That’s odd. I’ve never heard diff eq referred to as Calc 4. Integration by parts is really useful. I hope you feel derustified now. :^>

waterskier2007's avatar

idk. here we refer to it as that. i think its just cus in the sequence its the one after calc 3

cyndyh's avatar

It’s just that diff eq isn’t dependent on calc 3. You could just as easily take it after calc 2. You don’t have to have an understanding of the multi-variable stuff prior to understanding diff eq. What’s considered calc 5, 6, 7, ...? :^>

waterskier2007's avatar

umm linear algebra is after diff eq i believe

cyndyh's avatar

The point is that there’s a lot of other math that’s not just the next “calc” class. Cheers!

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