Choosing the Right Variable for Radius of Shell in Cylindrical Shell Method

[Jon1436]

Im new to finding volume using the cylindicral shell method so what should i do. I know I will eventually plug equations into the integral 2piX(f(x)-g(x))dx

x=y x+2y=3 and y=0 revolve about the x axis

 

[Dick]

Draw a picture of the region. Now visualize what the shells are going to look like around the region. Then take your formula and think of it as 2*pi*(radius of shell)*(length of shell)*d(radius of shell). If you are rotating around the x-axis, which variable is a good choice for radius of shell. x or y?