In this section we are learning about revolving a function around an axis. The most important part of this is being able to visualize it! To make that a little easier, I found some animations online that will be a good starting place.
Please visit this link and look at the first three animations more closely by pressing "Replay the animation". Notice what kind of shapes are made as the graph is being revolved.
What kind of shape does the revolution make if there are TWO functions?
More animations if you want to see them: