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# Integration by parts help watch

1. There's an integral I don't know how to do and I'm told that I'm to use integration by parts. It's the integral of x^7 divided by sqrt(x^4 + 9).
I know that if I let u = x^2 / 3 then I have 27/2 multiplied by the integral of u^3 divided by sqrt(u^2 + 1). But I don't know where to go from here.
2. (Original post by UpstairsMuffin)
There's an integral I don't know how to do and I'm told that I'm to use integration by parts. It's the integral of x^7 divided by sqrt(x^4 + 9).
I know that if I let u = x^2 / 3 then I have 27/2 multiplied by the integral of u^3 divided by sqrt(u^2 + 1). But I don't know where to go from here.
Try using integration by parts with and (this is a standard form f'(x)f(x)^n to integrate.
3. (Original post by Zacken)
Try using integration by parts with and (this is a standard form f'(x)f(x)^n to integrate.
Then I end up with the integral of (u^2 + 1)^3/2. :/
4. (Original post by UpstairsMuffin)
Then I end up with the integral of (u^2 + 1)^3/2. :/
Did you? Mind showing me your working? That doesn't seem correct.
5. (Original post by Zacken)
Did you? Mind showing me your working? That doesn't seem correct.
With a whole bunch of other stuff added to it from the IBP, I mean.
6. (Original post by UpstairsMuffin)
With a whole bunch of other stuff added to it from the IBP, I mean.
It's the whole other stuff that makes it very easy to integrate.
7. (Original post by Zacken)
It's the whole other stuff that makes it very easy to integrate.
go and do some STEP papers ... otherwise I can see you in Warwick ...
(you spend too long in here)
8. (Original post by Zacken)
It's the whole other stuff that makes it very easy to integrate.
The whole other stuff is outside of the integral.
9. (Original post by TeeEm)
go and do some STEP papers ... otherwise I can see you in Warwick ...
(you spend too long in here)
I've done lots of integrals, I just find this one very difficult.
10. (Original post by TeeEm)
go and do some STEP papers ... otherwise I can see you in Warwick ...
(you spend too long in here)
I'm not at home, having dinner out! Can't do STEP right now.
(I do though, you have a point)

(Original post by UpstairsMuffin)
The whole other stuff is outside of the integral.
Please show us your working, the other stuff should not be outside the integral. You should have inside the integral. Sorry for the bad LaTeX, it's very hard to type on a phone.
11. (Original post by Zacken)
It's the whole other stuff that makes it very easy to integrate.
Talk to your family I'm sure they're nice people.
12. (Original post by Zacken)
I'm not at home, having dinner out! Can't do STEP right now.
(I do though, you have a point)

Please show us your working, the other stuff should not be outside the integral. You should have inside the integral. Sorry for the bad LaTeX, it's very hard to type on a phone.
13. (Original post by UpstairsMuffin)
Huh? You're using integration by parts on with and

So using the integration by parts formula (look this up, I think you're getting it wrong!) you should get:

(I really hope that latex works...)
14. (Original post by Zacken)
Huh? You're using integration by parts on with and

So using the integration by parts formula (look this up, I think you're getting it wrong!) you should get:

(I really hope that latex works...)
Aha! Thank you! I just got confused over what I was differentiating and what I was antidifferentiating. It's easy to lose track of what you're doing when you're trying to do so many things in your head at once. That one mistake caused me a lot of pain. That's it now, thanks.
15. (Original post by UpstairsMuffin)
Aha! Thank you! I just got confused over what I was differentiating and what I was antidifferentiating. It's easy to lose track of what you're doing when you're trying to do so many things in your head at once. That one mistake caused me a lot of pain. That's it now, thanks.
16. (Original post by TeeEm)
go and do some STEP papers ... otherwise I can see you in Warwick ...
(you spend too long in here)

Even I was keen not to end up at Warwick; the university just seems a bit low-profile in comparison to Oxbridge, Imperial, UCL and so on.

But our Zacken will definitely end up at Cambridge
17. (Original post by Zacken)
I'm not at home, having dinner out! Can't do STEP right now.
(I do though, you have a point)

Please show us your working, the other stuff should not be outside the integral. You should have inside the integral. Sorry for the bad LaTeX, it's very hard to type on a phone.
Omg you're having dinner out and you're on your phone helping out on the maths forum?

Definition of dedication xD (or addiction )
18. (Original post by Indeterminate)

Even I was keen not to end up at Warwick; the university just seems a bit low-profile in comparison to Oxbridge, Imperial, UCL and so on.

But our Zacken will definitely end up at Cambridge
remember what happened to physicsmaths last year ...
19. (Original post by Student403)
Omg you're having dinner out and you're on your phone helping out on the maths forum?

Definition of dedication xD (or addiction )
both !!
20. (Original post by TeeEm)
both !!
Yes!

Zacken surely your main course is here by now?! Get off and enjoy your dinner out

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