Use the techniques from integration to find the volume of a cylinder of height h and radius r I was thinking of starting with a quadrilateral or rectangle.
starting with a horizontal line a  $y = r$, then set the area under the curve by integrating from $0$ to $h$.
$y=r$ then $y = r^2$
$$\pi \int_{0}^{h} r^2 $$
how's this?

Actually I don't have any plotting software with me but soon I'll show you Images that'll help understanding these methods
Solution 1
Assuming that You know that Area of Circle with radius R is $\pi R^2$
Now consider a disc (differential element)  of Radius $R$ and Thickness $dh$
It's volume will be $$ dv=\pi R^2 dh$$
Volume of cylinder can be written as $$V=\int_0^H dv=\int_0^H\pi R^2 dh={\pi R^2 H}$$
Solution 2
Assuming that you know that cirumference of circle with radius R is $2\pi R$
Now consider a cylindrical layer ( differential element ) at distance $r$ from center with thickness $dr$ 
It's volume will be $$dv=2\pi r H dr$$
Volume of cylinder can be written as $$V=\int_0^R dv=\int_0^R 2\pi Hr dr=\frac{2\pi R^2 H}{2}={\pi R^2 H}$$
If possible I'll add more methods.
