Argh, I can't integrate this...

[Pennycook]

I'm trying to integrate (x+3) / (x+2), as you do... But I can't. I know what the answer is, but I don't know how to get to it. I've tried integration by parts and it just went wrong...

I feel like such an idiot, because I could integrate pretty much anything else. Lol.

Anybody help? ^_^;;

[TheAnimus]

quotient rule:

http://www.mathsnet.net/asa2/modules/p34quotient.html

great site, set up for edexcel rather than MEI (who i sat. Wow, feals like it was 10 years, but was only 3!)

[Pennycook]

quotient rule:

http://www.mathsnet.net/asa2/modules/p34quotient.html

great site, set up for edexcel rather than MEI (who i sat. Wow, feals like it was 10 years, but was only 3!)

The quotient rule is for differentiation. ^_^;;

Thanks anyway, though.

[TheAnimus]

hehe silly me, sorry, mind not in gear, you want to it by parts. you should get:

= x + log (x + 2) + 2 + c

edit: my bad, forgot + c!

brain is in a state today, i think it needs nice cold larger. (preferably from belgium)

[Pennycook]

hehe silly me, sorry, mind not in gear, you want to it by parts. you should get:

= x + log (x + 2) + 2 + c

edit: my bad, forgot + c!

brain is in a state today, i think it needs nice cold larger. (preferably from belgium)

That's what I'm supposed to get, but for some reason I can't... Could you show me how you've done parts, please? I kept going in circles. ^_^;;

[keith.ftm]

I'm trying to integrate (x+3) / (x+2), as you do... But I can't. I know what the answer is, but I don't know how to get to it. I've tried integration by parts and it just went wrong...

I feel like such an idiot, because I could integrate pretty much anything else. Lol.

Anybody help? ^_^;;

Why?

[TheAnimus]

what form are you putting it in.
I'm guessing this is maths homework, so i shouldn't help you cheat, you've got plenty of time before 6th form tommorow (appologies if its more important than this).

And i'm reloading my tablet PC, and i hate inputing maths with Keyboard + Mouse (give me tablet equation tool every time baby!)

[Pennycook]

Why?

Why what?

TheAnimus: Yes, it is Maths homework, but it really wouldn't be cheating. I've been GIVEN the answer and I know that I have to do it by parts. But when I do it by parts, I'm going wrong somewhere. I just want to know where. ^_^;;

[keith.ftm]

Why...........

Why do you want to integrate (x+3) / (x+2)?

Seen the new posts now so question answered! Was just interested.

[herulach]

u = (x+3)
v = (x+2)
u' = (x)
v' = (x)

(uv'-vu')/v^2= (x^2+3x-x^2-2x)/x^2

simple (although ive probably done it wrong, mumbles something about it being because its too easy)

[Pennycook]

u = (x+3)
v = (x+2)
u' = (x)
v' = (x)

(uv'-vu')/v^2= (x^2+3x-x^2-2x)/x^2

simple (although ive probably done it wrong, mumbles something about it being because its too easy)

You've differentiated it. ^_^;;

[herulach]

You've differentiated it. ^_^;;

yeah, i just realised that doh

[Pennycook]

It's not just that question, either... I can DO parts. I know I can do parts. But there are just some questions that seem to confuse the hell out of me; I'll do parts, end up going in circles, or do parts twice and be no better off.

[Twigman]

u dv/dx = uv - Svdu/dx

(x+3) / (x+2) = (x+3) * 1/(x+2)

try that.

Or partial fractions then integrate it.

How far have you got?

EDIT: you do mine, and I'll do yours. http://forums.hexus.net/showthread.php?p=639447 deal?

[Pennycook]

u dv/dx = uv - Svdu/dx

(x+3) / (x+2) = (x+3) * 1/(x+2)

try that.

Or partial fractions then integrate it.

How far have you got?

EDIT: you do mine, and I'll do yours. http://forums.hexus.net/showthread.php?p=639447 deal?

That's what I've been trying... u = (x+3), v' = (x+2)^-1

Therefore, S u.v' = (x+3).ln(x+2) - S ln(x+2)

However, then I get stuck, because in order to integrate ln(x+2) I have to set it as u with v' as 1... It just goes around in circles.

EDIT: I have no idea what that thread's even talking about. I'd also like to clarify that I'm not looking for somebody to do my homework for me... I KNOW the answer, I know how I'm supposed to be doing it, I just want to see it worked so I can see where I'm going wrong on this question and on all of the others like it.

[smtkr]

Look:

u=(x+3), du=dx, dv=(1/(x+2))dx, v=ln(x+2)

1. integral ((X+3)/(x+2))=uv-integral(v*du)=(x+3)*ln(x+2)-integral(ln(x+2)dx)

Now, the bolded part is just simple substitution and an identity:

2. u=(x+2); integral(ln(u)du) = u*ln(u) - u = (x+2)*ln(x+2) - (x+2)

Plug 2. in for the bolded part and you get:

3. (x+3)*ln(x+2) - ((x+2)*ln(x+2) - (x+2)) = ln(x+2) + x + 2 + C