# [SOLVED] volume by cylindrical shell

• Jan 26th 2009, 04:59 PM
mollymcf2009
[SOLVED] volume by cylindrical shell
I originally posted this in Calculus section and I don't know how to delete it. Can someone do that for me please? I'm getting close to my deadline, so I really need someone to check that I have my integral set up correctly. I can not get the right answer

Bounding curves:

$y = 8 - x^2$ and $y = x^2$

Find volume of region bounded by these curves when rotated about x = 2

I wrote my integral as:

$\int\limits_{-2}^{2} (2-x)((8-x^2)-(x^2)) dx$

Look okay?
• Jan 26th 2009, 05:30 PM
Soroban
Hello, mollymcf2009!

Quote:

Bounding curves: . $y \:= \:8 - x^2 \,\text{ and }\,y \:=\: x^2$
Find volume of region bounded by these curves when rotated about $x = 2.$

I wrote my integral as: . $\int_{-2}^2 (2-x)\left[(8-x^2)- x^2\right]\,dx$

Look okay?

Probably an oversight, but you need ${\color{red}2\pi}$ in front . . . The rest is fine!

• Jan 26th 2009, 05:36 PM
mollymcf2009
Thank you so much!! Yes, I usually just move the $2\pi$ out immediately so I forgot to add that.
Thanks again!!
• Jan 26th 2009, 07:18 PM
mr fantastic
Quote:

Originally Posted by mollymcf2009
I originally posted this in Calculus section and I don't know how to delete it. Can someone do that for me please?

Done. Next time, please do the following:

1. Repost the unwanted post using the Report Post tool found top right.
2. Edit the unwanted post to something like "Please delete, post reported".