- #1
Jovy
- 17
- 2
Homework Statement
Find the volume of the solid generated by revolving the region bounded by the graphs of the equations about the line y =4.
$$y=\frac 3 {1+x},~ y=0,~ x=0,~x=3$$
Homework Equations
$$V= \int_a^b ([R(x)]^2-[r(x)]^2)dx$$
The Attempt at a Solution
I understand how to use the equation, but I don't know how to find all the components needed to plug into the equation. R(x) and r(x) are both the inner and outer radius, however, I don't understand why R(x)=4 and ##r(x)=4-\frac 3 {1+x}##. I understand that (a,b) are (0,3) since that is what x equals. I'm just having trouble understanding the radius.
This website showed how to solve the problem, but it doesn't really explain each step.
http://www.calcchat.com/book/Calculus-ETF-6e/7/2/17/