Doug C. answered • 12/07/19
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This video does not show the manual evaluation of the definite integrals, but does show how to set them up for both washer and shell methods.
Drew M.
*Doug
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12/07/19
Doug C.
So the axis of revolution does not have to be the x-axis or y -axis, it can be any horizontal or vertical line. So let's say the axis of revolution is the line x = -3 and you are using the shell method and integrating along the x-axis from 1 to 4 (for example). The shell method requires you to come up with an expression for the "average radius". The right-hand end point of a typical radius will be represented by "x". The distance from the axis or revolution to that x-value you can think of as right-hand endpoint minus left-hand endpoint, in this example that would be x - (-3) or x + 3.
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12/08/19
Drew M.
Thank you for help setting up this equation doug. I was confused because I'm used to problems stating "about the 'blank' axis" so I wanted to know if x=-1 is suppose to lead me to believe its about the y-axis in this case? I got my answer pi/2 but i just wanted to know why it didn't say about any axis. Sorry I'm still new to these concepts!12/07/19