# Volume of revolution

1. Jan 23, 2007

### ductape

The question I need to solve for an assignment is as follows:
Find the volume of the solid that is obtained by revolving the region R around the x-axis.

I figured that the volume would just be the integral of pi R^2 dx, so that would just be pi R^2 x, but that is not the answer. I suspect I am misinterpreting the question.

2. Jan 23, 2007

### cristo

Staff Emeritus
Well, R is probably a function of x. If you write the question, as stated, then we'll be more able to help you!

3. Jan 23, 2007

### ductape

My problem is that that is the problem as stated. It doesn't give a function in terms of x.

4. Jan 23, 2007

### ductape

Ah nevermind, I found out that the question was referring to an area already found in a previous question.

5. Jan 23, 2007

### Gib Z

Yes, and if it didn't specify the function, it would be $$\pi\int^b_a R^2 dx$$ anyway, where R is the closed interval (a,b).

6. Jan 24, 2007

### HallsofIvy

Even that wouldn't make sense! If R is an interval it is not a number! I think both you and ductape are confusing the interval R with "radius" R.