# Homework Help: Volume of revolution problem

1. Feb 15, 2006

### G01

Find the volume created by revolving:
$$y=x^2 +x - 2$$

and y=0 about the x axis.

$$y=x^2 +x - 2$$ intersects the x axis at -1 and 1 so those are the bounds of integration.

the radius of the figure = -($$y=x^2 +x - 2$$)

so:

V = $$- \pi \int_{-1}^1 (x^2 + x - 2)^2 dx$$

After integrating that I get 18$$\pi$$/5. The actual answer is 81$$\pi$$/10. What I want to know is if i set the integral up right. If I did then this is only a stupid integration mistake. If not then I hope someone finds my mistake. Thanks for the help.

2. Feb 16, 2006

### TD

You may want to check that again
Fix this, and you'll find the given answer.