Volume of revolution, where am i going wrong?

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Homework Help Overview

The problem involves finding the volume of a solid obtained by rotating a region bounded by the curves y=x^2, y=4, and x=0 about the line x=-2 using the shell method. The original poster expresses confusion regarding the discrepancy between results obtained using different methods.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to apply the shell method and provides an integral setup, while expressing uncertainty about the correctness of their answer compared to the disk method. Some participants question the validity of the original poster's reasoning regarding the correctness of their results.

Discussion Status

Some participants have indicated agreement with the original poster's shell method result, suggesting that there may be a misunderstanding or error in the original poster's calculations. The discussion appears to be exploring the differences in results without reaching a definitive conclusion.

Contextual Notes

The original poster's confusion stems from differing results obtained through the shell method and the disk method, with no explicit consensus on the correct answer being reached in the discussion.

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Homework Statement


Find the volume of solid obtained by rotating the region bounded by y=x^2,y=4 and x=0 about the line x=-2 using the shell method.

Homework Equations


I'm stuck because using disks I got the right answer 136pi/3 but I can't using shells?


The Attempt at a Solution


Integral 2pi (2+x) (4-x^2) dx from x=0 to 2. This gives 88 pi/3..

Please help!
 
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Why do you think ##136\pi/3## is correct? Your ##88\pi/3## looks correct to me. Hard to say what mistake you make, not seeing your work.
 
I agree, the correct answer is 88/3 *pi
 

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