Originally Posted by

**s_ingram** Hi SlipEternal,

I am somewhat embarrassed here!

Surely the area of a single disk of radius $y_{1} - y_{2}$ (where $y_{1} \gt y_{2}$) is the same as the difference in area of two disks, one with radius $y_{1}$ and the other $y_{2}$? It represents the same washer.

In this example I don't actually have a washer, I have a disk. If you look at my diagram, there is no hole. The area between the curve and line is continuous from x = 0 to x = 2. According to Skeeter's diagram for a disk $V = \int_{a}^{b} \pi [R(x)]^2$ where $R(x) = y_{1} - y_{2}$. This is the method that get's me the wrong answer.