Area by Parts and Rotational Volume
Washer Method
When finding the volume two enclosed functions yield by rotating around an axis we use the washer method. It involves subtracting one area by disk from another area by disk.
For example:
3.1 Let R denote the area enclosed by 
. Find the volume of R when it is spun around the x axis. (when x ≥ 0, y ≥ 0)
Intersect when y1 = y2
Throw out the negative 1 because it is less than 0.
Rotating around a line rather than an axis with disk:
The distance between the axis and the line you are rotating around gets added to the function.
For example:
3.2 Find the volume of the function 
rotated about the line 
The + 3 is inserted since it is rotating around 
which is three units away from the y axis
