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## Homework Statement

Hi, well, I don't have to solve any problem yet. I have an inquietude about solids of revolution. I've been reading this: http://en.wikipedia.org/wiki/Solid_of_revolution and this: http://en.wikipedia.org/wiki/Disk_integration

What I wanted to know is if its the same this equation than the other:

This one:

Wikipedia said:Function of y

If the function to be revolved is a function of y, the following integral will obtain the volume of the solid of revolution:

[tex]\color{red}\pi \int_c^d {\left[R(y)\right]}^2\ \mathrm{d}y[/tex]

And this one:

Wikipedia said:Cylinder method

The cylinder method is used when the slice that was drawn is ''parallel to'' the axis of revolution; i.e. when integrating ''perpendicular to'' the axis of revolution.

The volume of the solid formed by rotating the area between the curves of [tex]f(x)[/tex] and [tex]g(x)[/tex] and the lines [tex]x=a[/tex] and [tex]x=b[/tex] about the ''y''-axis is given by

[tex]\color{red}}V = 2\pi \int_a^b x f(x)\,dx[/tex]

I think I'm getting it now... The second one is to derive the function under the curve (or between the curve and the X axis) around the Y axis, and the first derives between the curve and the Y axis around the Y axis. Is that right?

Bye, and thanks off course.

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