Hi All, I had a question about this problem I was doing and was hoping to see if I did it right.(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

Using Disk or Washer method Find volume of the solid generated by revolving the region bounded by y=sqrt(x), y=2, x=0 about the line y=2.

2. Relevant equations

Disk Method: pi*Integral (R(x))^2dx where R(x) is the distance from the axis of revolution to the regions boundaries.

3. The attempt at a solution

Limits of integration are [0,4]

I was getting caught up with what R(x) is. Since I am revolving up around y=2 I am wondering if the distance is 2-sqrt(x) or sqrt(x)-2

Doing the problem with R(x)=sqrt(x)-2 I get:

8pi/3

Doing the problem with R(x) = 2-sqrt(x) I get:

8pi/3 again...

So what I am wondering is, in the future, which one is the correct R(x)? or does it not matter? I feel like it should be 2-sqrt(x) because that more clearly sticks out to me as the radius but im not sure.

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# Homework Help: Calc2: Solid of revolution about y=2 question

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