bits n bobs

**Amanda-UK** · August 22nd 2007, 06:17 AM

few little grey areas:

1) how would i work this one out:

find the vloume generated by rotationg the area bounded by y=x^2 and y=4 around the line y=1

**ThePerfectHacker** · August 22nd 2007, 07:38 AM

It is the same as rotating $(x+1)^2$ around $y=0$ . Use the volume of rotation formula.

**Amanda-UK** · August 22nd 2007, 08:44 AM

Originally Posted by ThePerfectHacker

It is the same as rotating $(x+1)^2$ around $y=0$ . Use the volume of rotation formula.

what formula is that?
x

**Rebesques** · August 22nd 2007, 08:56 AM

$\int_a^b \pi f^2(x)dx$ .

**ThePerfectHacker** · August 22nd 2007, 09:04 AM

Originally Posted by Rebesques

$\int_a^b \pi f^2(x)dx$ .

It should be,
$2\pi \int_a^b xf(x) dx$

**Rebesques** · August 22nd 2007, 12:19 PM

I doubt it

This random page says otherwise:

Volume of A Solid of Revolution

Are you talking about surface area maybe?

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