Prove Guldin's laws

[Vadi]

I want to prove Guldin's laws using a cylindre.

Guldin's law:
Volume of a rotated body=
Pi*Area of the rotating crossection*Length of the path of the centre of gravity of the rotating crossection

In order to prove it, it should be equal to the Volume of a Cylinder:
Volume of a cylinder=
r*r*h*Pi

Somehow I can't figure it out.

Can somebody help please?


Greetings,

Sladan