# Volume integral question

1. Jan 5, 2014

### ppy

Hi,

I was attempting a volume integral question out of a book. I know what the final answer is and what integral i am supposed to work out but I do not know how I am supposed to solve it. I have tried different ways such as integration by substitution and integration by parts but I do not seem to be getting anywhere.

This is the ∫$^{1}_{-1}$ 4(√(1-x$^{2}$))(x+1)dx The answer is 2pi.

any help would be great thanks.

Last edited by a moderator: Jan 5, 2014
2. Jan 5, 2014

### davidmoore63@y

This is not a volume integral. Put x=sin u and proceed

3. Jan 5, 2014

### ppy

The integral started out as a triple volume integral. The part mentioned is the final part of the triple integral. I have tried x=sinu and still got nowhere. Is it a simple substitution or do I have to integrate by parts as well ?
Thanks

4. Jan 5, 2014

### tiny-tim

hi ppy!
davidmoore63@y's substitution does work …

show us how far you got with it

5. Jan 5, 2014

### ppy

Thanks. I've got there now !

6. Jan 5, 2014

### Staff: Mentor

The presence of the $\sqrt{1 - x^2}$ factor suggests that a trig substitution is called for, and that's the direction that davidmoore and tiny-tim are recommending.

BTW, there are no such words in English as "intergral", "intergrate", or "intergration".