Barrons AP Calculus

Figure  N7–13

SOLUTION:
Disk.

See Questions 18, 49, 51, 52, and 53 in the Practice Exercises for examples of
finding volumes by disks.

WASHERS

A washer is a disk with a hole in it. The volume may be regarded as the
difference in the volumes of two concentric disks. As an example, consider the
volume of the solid of revolution formed when the region bounded by the two
curves seen in Figure N7–14 is revolved around the x-axis. We think of the
rectangular strip of the region at the left as generating the washer, ΔV (an
element of the volume), shown at the right.

Washers