# Integration, U substitution help

1. Jul 22, 2011

### Dragonetti

1. The problem statement, all variables and given/known data

Hi I am having a few problems with the below u substitution can anyone help,
In particular what to do with the integral of the u substitution?

2. Relevant equations

$\int$2x2 square root of 1-x3 dx, u = 1-x3

Any pointers would be appreciated
Thanks
D

2. Jul 22, 2011

### Stengah

Once you have u just take the derivative of it and substitute it back in for dx. The u is right and I can see that it will work out just fine. Try reviewing an example from your notes or the textbook.

3. Jul 23, 2011

### nickalh

Can you show us the work you've done so far?
The next step is to find du/dx.
Create something in the integral which we can replace (...)dx and put in du.
Can you show what you get for du/dx?

Last edited by a moderator: Apr 26, 2017
4. Jul 23, 2011

### Dragonetti

Hi Thanks for the help much appriciated,

I think I have worked it out, answer below;

-4/9(1-x3)3/2 du?

I have differentiated it and I get back to original answer.

Just one thing, if my original limits were 2,1 would my new limits be -7,0?

Thanks again
Dominic

5. Jul 23, 2011

### Stengah

You got it except you don't need the du at the end. And actually you need your +C as well. But I don't know what you mean with your question regarding limits.

6. Jul 23, 2011

### nickalh

Yes, that's right.