Figure N7–14This washer’s height is the thickness of the rectangular strip, Δx. The washer
is a disk whose outer radius, R, is the distance to the top of the rectangular strip,
with the disk of inner radius r (the distance to the bottom of the strip) removed.
Thus: .
Example 8 __
Find the volume obtained when the region bounded by y = x^2 and y = 2x is
revolved about the x-axis.
SOLUTION: The curves intersect at the origin and at (2, 4), as shown in Figure
N7–15. Note that we distinguish between the two functions by letting (x, y 1 ) be a
point on the line and (x, y 2 ) be a point on the parabola.
Washer.